Wire cross-section by diameter: formulas and tables

General information about cable and wire

When working with conductors, it is necessary to understand their designation.
There are wires and cables that differ from each other in their internal structure and technical characteristics. However, many people often confuse these concepts. A wire is a conductor that has in its design one wire or a group of wires woven together and a thin common insulating layer. A cable is a core or a group of cores that has both its own insulation and a common insulating layer (sheath). Each type of conductor will have its own methods for determining cross sections, which are almost similar.

Conductor materials

The amount of energy that a conductor transmits depends on a number of factors, the main one of which is the material of the current-carrying conductors. The following non-ferrous metals can be used as the core material of wires and cables:

Aluminum. Cheap and lightweight conductors, which is their advantage. They are characterized by such negative qualities as low electrical conductivity, a tendency to mechanical damage, high transient electrical resistance of oxidized surfaces;
Copper. The most popular conductors, which have a high cost compared to other options. However, they are characterized by low electrical and transition resistance at the contacts, fairly high elasticity and strength, and ease of soldering and welding;
Aluminum copper. Cable products with aluminum cores coated with copper. They are characterized by slightly lower electrical conductivity than their copper counterparts. They are also characterized by lightness, average resistance and relative cheapness.

Some methods for determining the cross-section of cables and wires will depend specifically on the material of their conductor component, which directly affects the throughput power and current strength (method of determining the cross-section of conductors by power and current).

Calculation of the cross-section of a stranded conductor

Stranded wire consists of several individual wires. Its cross section is calculated as follows:

The indicator of the cross-sectional area of one core is found.
Cable cores are recalculated.
The quantity is multiplied by the cross-section of one core.

When connecting a stranded conductor, its ends are crimped with a special sleeve using crimping pliers.

Features of electrical wires

With all the variety of cable products and a huge selection of wires for laying electrical networks, there are selection rules. It is not necessary to memorize all brands of cables and wires; you need to be able to read and decipher their markings. First, it’s worth figuring out the difference between a wire and a cable.

Wire – A conductor used to connect two sections of a circuit. May have one or more conductive wires. The veins can be:

naked;
isolated;
single-core;
stranded.

Bare lines are used where touching live wires is impossible. In most cases they are used for overhead power lines.

The insulating coating is used in one or two layers. Wires that have two or three conductors in double insulation are confused with a cable. The confusion occurs due to the fact that insulation covers each core, and on the outside there is a general polymer or other coating. Such conductors are used inside electrical devices, panels or cabinets. In everyday life, they are hidden in the wall or laid in special channels.

Insulated products are used everywhere. Depending on the degree of electrical safety of the room and the installation location, the insulation class is selected.

Stranded conductors are used where small radius bends are required when laying complex routes where single-core analogues cannot pass. This type of current conductors is convenient to install in cable ducts. Single-core wires are more difficult to bend in such conditions, force must be applied, and there is a risk of damage to the wire.

For your information. Marking APPV 3*2.5 means a wire with aluminum conductors, polyvinyl chloride insulation, flat, having a dividing base. The meaning of the marking is clarified in the reference literature.

In terms of structure, a cable consists of several individually insulated strands placed in a protective outer layer of dielectric material. The space between the cores and the shell is filled with paper tapes, plastic threads or cable yarn to prevent sticking. Additionally, the product can be reinforced with armor made of tapes or steel braiding to protect against mechanical damage.

Conductor cross-sectional area

Calculation of voltage drop in a cable. In drawings, a section is an image of a figure formed by cutting a part with a plane. What is a cross section in electrical engineering? Applicable to electricity, considers the cross-section of a conductor at right angles to its longitudinal side. The cross-section of the core through which electrons pass is a circle and is measured in mm2. Important! The diameter of the core is often confused with its cross-section. To find out what cross-section the wire has, you need to determine the area of the resulting circle by calculating it using the formula.

Conductor cross section

Since the cross-section of the wire is a circle, the area is calculated using the formula:

S cr = π*R2, where:

S cr. – area of the circle, mm2;
π = 3.14;
R – radius of the circle, mm.

Knowing the cross-sectional area of the core, its length and the resistivity of the material from which it is made, it is possible to calculate the resistance of the conductor to the electric current flowing through it.

Information. Considering that the radius is equal to 1/2 the diameter, the formula can be transformed for ease of use. It will look like Skr = π*D2/4 = 0.8 * D2. To calculate the cross-sectional area of a conductor, the diameter value is often used. An incorrectly selected wire diameter causes it to overheat and melt, which, in turn, can cause a fire in the electrical wiring.

How to find out the cross-section of a wire by its diameter for a stranded or segmented cable

If determining the diameter for a single-core conductor does not cause any problems, then measuring a stranded or segmented conductor can cause certain difficulties.

Measuring the cross-section of a stranded wire

When determining the core diameter of a given cable, you cannot measure this size for all wires of the core at once: the value will be inaccurate, since there is space between the wires. Therefore, this cable must first be stripped of insulation, then the stranded conductor must be fluffed up and the number of wires in the core must be counted. Next, using any method (calipers, ruler, micrometer), measure the diameter of one core and determine the cross-sectional area of the wire. After this, the resulting value is multiplied by the number of wires in the bundle and the exact size of the existing conductor is obtained.

Segment conductor measurement

Determining the dimensions of a segmented conductor is somewhat more difficult than measuring a round solid or stranded cable. In order to correctly estimate the cross-sectional area of such a conductor, it is necessary to use special tables. For example, to calculate the cross-sectional area of an aluminum conductor segment, determine the height and width of the segment and use the following table:

Cable		Sectional area of the segment, mm2
35	50	70	95	120	150	185	240
Three-core sector single-wire, 6(10) kV	high	5,5	6,4	7,6	9	10,1	11,3	12,5	14,4
Three-core sector single-wire, 6(10) kV	shire	9,2	10,5	12,5	15	16,6	18,4	20,7	23,8
Three-core sector stranded, 6(10) kV	high	6	7	9	10	11	12	13,2	15,2
Three-core sector stranded, 6(10) kV	shire	10	12	14	16	18	20	22	25
Four-core sector single-wire, up to 1 kV	high	–	7	8,2	9,6	10,8	12	13,2	–
Four-core sector single-wire, up to 1 kV	shire	–	10	12	14,1	16	18	18	–

Dependence of current, power and core cross-section

It is not enough to measure and calculate the cross-sectional area of the cable based on the diameter of the core. Before installing wiring or other types of electrical networks, it is also necessary to know the capacity of the cable products.

the strength of the electric current that the cable will pass;
consumer power;
current load exerted on the cable.

Power

The most important parameter during electrical installation work (in particular, cable laying) is throughput. The maximum power of electricity transmitted through it depends on the cross-section of the conductor. Therefore, it is extremely important to know the total power of the energy consumption sources that will be connected to the wire. Typically, manufacturers of household appliances, appliances and other electrical products indicate on the label and in the documentation accompanying them the maximum and average power consumption.

For example, a washing machine can consume electricity ranging from tens of W/h during rinsing mode to 2.7 kW/h when heating water.

Accordingly, a wire with a cross-section that is sufficient to transmit electricity of maximum power must be connected to it. If two or more consumers are connected to the cable, then the total power is determined by adding the limit values of each of them. The average power of all electrical appliances and lighting devices in an apartment rarely exceeds 7500 W for a single-phase network. Accordingly, the cable cross-sections in the electrical wiring must be selected to this value.

It is recommended to round the cross-section towards higher power due to a possible increase in power consumption in the future. Typically, the next largest cross-sectional area from the calculated value is taken. So, for a total power of 7.5 kW, it is necessary to use a copper cable with a core cross-section of 4 mm2, which is capable of transmitting about 8.3 kW. The cross-section of the conductor with an aluminum core in this case must be at least 6 mm2, passing a current power of 7.9 kW.

Selection by table

Knowing the diameter of the wire, you can determine its cross-section using a ready-made dependence table. The table for calculating the cable cross-section by core diameter looks like this:

Conductor diameter, mm	Conductor cross-section, mm2
0.8	0.5
1	0.75
1.1	1
1.2	1.2
1.4	1.5
1.6	2
1.8	2.5
2	3
2.3	4
2.5	5
2.8	6
3.2	8
3.6	10
4.5	16

When the cross-section is known, it is possible to determine the permissible power and current values for copper or aluminum wire. In this way, it will be possible to find out what load parameters the current-carrying core is designed for. To do this, you will need a table of the dependence of the cross section on the maximum current and power.

In the air (trays, boxes, voids, channels)						Section, sq. mm	In the ground
Copper conductors			Aluminum conductors				Copper conductors			Aluminum conductors
Current. A	power, kWt		Tone. A	power, kWt			Current, A	power, kWt		Current. A	Power, kWt
Current. A	220 (V)	380(V)	Tone. A	220(V)	380(V)		Current, A	220(V)	380(V)	Current. A	220(V)
19	4.1	17.5	1,5	77	5.9	17.7
35	5.5	16.4	19	4.1	17.5	7,5	38	8.3	75	79	6.3
35	7.7	73	77	5.9	17.7	4	49	10.7	33.S	38	8.4
*2	9.7	77.6	37	7	71	6	60	13.3	39.5	46	10.1
55	17.1	36.7	47	9.7	77.6	10	90	19.8	S9.7	70	15.4
75	16.5	49.3	60	13.7	39.5	16	115	753	75.7	90	19,8
95	70,9	67.5	75	16.5	49.3	75	150	33	98.7	115	75.3
170	76.4	78.9	90	19.8	59.7	35	180	39.6	118.5	140	30.8
145	31.9	95.4	110	74.7	77.4	50	775	493	148	175	38.5
ISO	39.6	118.4	140	30.8	97.1	70	775	60.5	181	710	46.7
770	48.4	144.8	170	37.4	111.9	95	310	77.6	717.7	755	56.1
760	57,7	171.1	700	44	131,6	170	385	84.7	753.4	795	6S
305	67.1	700.7	735	51.7	154.6	150	435	95.7	786.3	335	73.7
350	77	730.3	770	59.4	177.7	185	500	110	379	385	84.7

Converting watts to kilowatts

In order to correctly use the table of wire cross-section versus power, it is important to correctly convert watts to kilowatts.

1 kilowatt = 1000 watts. Accordingly, to obtain the value in kilowatts, the power in watts must be divided by 1000. For example, 4300 W = 4.3 kW.

Features of self-calculation

Independent calculation of the longitudinal section is performed on a core without an insulating coating. A piece of insulation can be moved or removed on a piece purchased specifically for testing. First you need to determine the diameter and find the cross section using it. Several methods are used for the work.

Using a caliper

The method is justified if the parameters of a truncated or defective cable are measured. For example, VVG may be designated as 3x2.5, but in fact be 3x21. Calculations are made as follows:

The insulating coating is removed from the conductor.
The diameter is measured with a caliper. You will need to place the wire between the legs of the instrument and look at the scale markings. The integer value is on top, the decimal value is on the bottom.
Based on the formula for finding the area of a circle S = π (D/2)2 or its simplified version S = 0.8 D², the cross section is determined.
The diameter is 1.78 mm. Substituting the value into the expression and rounding the result to hundredths, we get 2.79 mm2.

For domestic purposes, you will need conductors with a cross section of 0.75; 1.5; 2.5 and 4 mm2.

Using a ruler and pencil

Calculation of PS using a ruler and pencil.

If you don't have a special meter, you can use a pencil and ruler. Operations are performed with the test image:

An area of 5-10 cm is cleared of the insulating layer.
The resulting wire is wound around a pencil. Full turns are laid tightly, there should be no space between them, the “tails” are directed up or down.
Ultimately, a certain number of turns should be obtained; they need to be counted.
The winding is applied to the ruler so that the zero division coincides with the first winding.
The length of the segment is measured and divided by the number of turns. The resulting value is the diameter.
For example, it turned out 11 turns, which occupy 7.5 mm. When dividing 7.5 by 11, 0.68 mm is the cable diameter. The cross section can be found using the formula.

The accuracy of the calculations is determined by the density and length of the winding.

How to calculate pipe parameters

When building and furnishing a home, pipes are not always used to transport liquids or gases.

They often act as a building material - to create the frame of various buildings, supports for canopies, etc. When determining the parameters of systems and structures, it is necessary to calculate the various characteristics of its components.

In this case, the process itself is called pipe calculation, and it includes both measurements and calculations.

Why do we need calculations of pipe parameters?

In modern construction, not only steel or galvanized pipes are used. The choice is already quite wide - PVC, polyethylene (HDPE and LDPE), polypropylene, metal-plastic, corrugated stainless steel.

They are good because they do not have as much mass as their steel counterparts. However, when transporting polymer products in large volumes, it is advisable to know their weight in order to understand what kind of machine is needed.

The weight of metal pipes is even more important - delivery is calculated by tonnage. So it is advisable to control this parameter.

What cannot be measured can be calculated

It is necessary to know the outer surface area of the pipe to purchase paint and thermal insulation materials. Only steel products are painted, because they are susceptible to corrosion, unlike polymer ones. So you have to protect the surface from exposure to aggressive environments.

They are used more often for the construction of fences, frames for outbuildings (garages, sheds, gazebos, cabins), so the operating conditions are difficult, protection is necessary, therefore all frames require painting.

This is where the area of the surface to be painted is required - the outer area of the pipe.

When constructing a water supply system for a private house or cottage, pipes are laid from the water source (well or borehole) to the house - underground.

And still, to keep them from freezing, insulation is required. You can calculate the amount of insulation by knowing the outer surface area of the pipeline.

Only in this case it is necessary to take material with a substantial margin - the joints must overlap with a substantial margin.

The cross-section of the pipe is necessary to determine the throughput - whether this product can carry the required amount of liquid or gas. The same parameter is often needed when choosing the diameter of pipes for heating and plumbing, calculating pump performance, etc.

Inner and outer diameter, wall thickness, radius

Pipes are a specific product. They have an internal and external diameter, since their wall is thick, its thickness depends on the type of pipe and the material from which it is made. Technical specifications often indicate the outer diameter and wall thickness.

Pipe inner and outer diameter, wall thickness

Having these two values, it is easy to calculate the internal diameter - subtract twice the wall thickness from the external one: d = D - 2*S. If you have an outer diameter of 32 mm, a wall thickness of 3 mm, then the inner diameter will be: 32 mm - 2 * 3 mm = 26 mm.

If, on the contrary, there is an internal diameter and wall thickness, but an external one is needed, we add double the stack thickness to the existing value.

With radii (denoted by the letter R) it is even simpler - this is half the diameter: R = 1/2 D. For example, let’s find the radius of a pipe with a diameter of 32 mm. Just divide 32 by two, we get 16 mm.

Vernier caliper measurements are more accurate

What to do if there are no technical data for the pipe? To measure. If special accuracy is not needed, a regular ruler will do; for more accurate measurements, it is better to use a caliper.

Calculation of pipe surface area

The pipe is a very long cylinder, and the surface area of the pipe is calculated as the area of the cylinder. For calculations, you will need a radius (internal or external - depends on what kind of surface you need to calculate) and the length of the segment that you need.

Formula for calculating the side surface of a pipe

To find the lateral area of the cylinder, we multiply the radius and length, multiply the resulting value by two, and then by the number “Pi”, we obtain the desired value. If desired, you can calculate the surface of one meter, which can then be multiplied by the desired length.

For example, let’s calculate the outer surface of a piece of pipe 5 meters long, with a diameter of 12 cm. First, let’s calculate the diameter: divide the diameter by 2, we get 6 cm.

Now all quantities must be reduced to the same units of measurement. Since the area is calculated in square meters, we convert centimeters to meters. 6 cm = 0.06 m.

Next, we substitute everything into the formula: S = 2 * 3.14 * 0.06 * 5 = 1.884 m2. If you round it up, you get 1.9 m2.

Weight calculation

When calculating the weight of a pipe, everything is simple: you need to know how much a linear meter weighs, then multiply this value by the length in meters.

The weight of round steel pipes is in reference books, since this type of rolled metal is standardized. The weight of one linear meter depends on the diameter and wall thickness.

One point: the standard weight is given for steel with a density of 7.85 g/cm2 - this is the type recommended by GOST.

Round Steel Pipe Weight Table

In table D - outer diameter, nominal diameter - inner diameter, And one more important point: the weight of ordinary rolled steel is indicated; galvanized steel is 3% heavier.

Weight table for profiled square pipe

How to calculate cross-sectional area

Formula for finding the cross-sectional area of a round pipe

If the pipe is round, the cross-sectional area should be calculated using the formula for the area of a circle: S = π*R2. Where R is the radius (internal), π is 3.14. In total, you need to square the radius and multiply it by 3.14.

For example, the cross-sectional area of a pipe with a diameter of 90 mm. We find the radius - 90 mm / 2 = 45 mm. In centimeters this is 4.5 cm. We square it: 4.5 * 4.5 = 2.025 cm2, substitute it into the formula S = 2 * 20.25 cm2 = 40.5 cm2.

Methods for determining wire cross-section step by step

There are several ways to measure the cross-section by core diameter. If the wire is single-core, then measurements will be made immediately on it, but one conductor must be untangled from the cable coil. After this, it is cleared of insulation so that only metal remains.

To calculate the area of a circle through the radius, use the formula: S = π × R2, where:

π – constant equal to 3.14;
R is the radius of the circle.

But, due to the fact that from a practical point of view it is much easier to calculate a diameter equal to two radii, the calculation formula will take the following form: S = π × (D/2)2. Depending on the methods for measuring the diameter, such methods for calculating the cross section are distinguished.

By diameter using a caliper or micrometer

The most relevant option to measure the diameter are instruments such as calipers and micrometers. These devices allow you to measure the diameter as accurately as possible. To do this you will need a wire and a micrometer.

To do this, latch B is moved to the open position. The micrometer handle is unscrewed to such a distance that the wire easily fits in the space between probes A. Then, using handle G, the device is twisted until the ratchet operates. After this, readings are recorded on all three scales at point B.

In this example, the diameter is 1.4 mm, therefore, to calculate the cross-section, you need S = 3.14 × 1.4 × 1.4 / 4 = 1.53 mm². The same procedure for determining the cross section can be performed using a caliper. The advantage of this method is the ability to measure any round conductor, even if it is already installed and used to power any electrical device. The main disadvantage of the method is the high cost of the devices; naturally, purchasing them for a couple of measurements is completely impractical.

By diameter using a pencil or pen

This method of determining the cross-section is based on the fact that the wire has the same diameter along its entire length. Take a regular pencil, pen or felt-tip pen and wrap the wire around it in a spiral. To eliminate the thickness of the insulation, it must be cut along its entire length. The rings should be placed as tightly as possible; the larger the space between the rings, the lower the accuracy.

Since all wires have the same thickness, to determine the diameter of the copper wires, measure the length of the entire winding and divide by the number of turns. In this example, D = 15 mm / 15 turns = 1 mm, respectively, using the same calculation formula, we obtain a section S = 3.14 × 1 × 1 / 4 = 0.78 mm². Note that the more turns you make, the more accurately you determine the cross-section.

It is worth noting that the advantage of this method is that only available means can be used to determine the cross-section. The disadvantage is low accuracy and the ability to wind only thin conductors. In the example, a relatively thin wire was used, but the distance between the turns is already visible. Because of which the accuracy leaves much to be desired, it goes without saying that aluminum wire cannot be bent in this way.

By diameter using a ruler

Let’s immediately make a reservation that for measuring with a ruler you can only take a relatively thick wire; the smaller the thickness, the lower the accuracy. The diameter of the vein can be determined by thread or paper; the second option is the most preferable, as it gives greater accuracy.

Tear off a small strip and fold it over on one side. Thinner paper is preferable, so there is no need to fold the sheet several times. Then the paper is applied to the wire and wrapped around the circumference until the strip touches. At the point of contact, it is bent a second time and applied to the ruler for measurement.

Using the resulting circumference L, the vein diameter D = L / 2 π is found, and the cross section is calculated as shown earlier. This method of determining the cross-section is well suited for large aluminum conductors. But the accuracy in this method is the lowest.

By diameter using ready-made tables

This method is suitable for standard gauge wires. For example, you have already determined the diameter using one of the above methods. Then you use the table to determine the section.

Table 1: determination of cross section based on wire diameter:

Diameter and cross-section of wires in the table

At first glance, the use of such tables is not advisable, since the conductor tag indicates its main parameters, however, there are certain subtleties here too. The fact is that the parameters declared by the manufacturer do not always correspond to reality, but the parameters given in the table are absolutely objective.

If, when measuring the diameter, the result given in the table does not differ significantly from the declared one, then you are dealing with a high-quality wire, but there are cases when the cross-sectional area does not correspond to the measured diameter of the wire, in this case, using the table will allow you to avoid purchasing a low-quality cable.

Expert opinion

It-Technology, Electrical power and electronics specialist

Ask questions to the “Specialist for modernization of energy generation systems”

Wire cross-section and diameter: table | Advice from experts In order to avoid such unpleasant situations, it would be a good idea to measure the diameter of the core yourself before purchasing a wire and make sure that the declared characteristics correspond to the actual ones. Ask, I'm in touch!

Determining the wire cross-section of outlet lines

When determining the wire diameter for room wiring, consider the maximum load of consumers that can be turned on at the same time. Based on this power, the cross-section of the main lines that go from the meter and input circuit breakers to the distribution boxes is selected. These are the areas that will bear the total load of all connected consumers. Choose a wire with copper conductors of at least 6 mm2.

Branch conductors from distribution boxes to sockets are selected individually for each room. This takes into account household electrical appliances that can be connected to an outlet. The cross-section of the cores is selected with a margin of one order of magnitude. This is in case there is a need to power some kind of construction tool from an outlet: a hammer drill, a welding inverter.

If the total power of consumers in the room is 4 kW, then the conductor with a copper core feeding the outlet should have a cross-section of 2.5 mm².

Attention! The cross-section of the conductor must allow it to withstand the current load and not overheat during operation of household appliances. In practice, the device with the highest power is determined and the appropriate wire diameter is selected relative to the characteristics of the device.

As a result, it turns out that the outlet conductor with copper conductors for each socket will have a cross-section of 2.5 mm2. The main wire for wiring is taken with a cross-section of 6 mm². It should be taken into account that the entire electrical wiring circuit is carried out with wires having cores of the same material. Copper and aluminum strands cannot be twisted together.

Tables for selecting a suitable conductor

A convenient and practical option for selecting the desired wire (cable) is to use special tables that indicate the diameters and cross-sections relative to the power and/or currents carried.

Having such a table at hand is an easy and simple way to quickly determine the conductor for the required electrical installation. Determining the required values using a classic table is one of the most convenient ways to select the required conductor during installation work. Considering that traditional conductors for electrical installations are products with copper or aluminum conductors, there are tables for both types of metals.

Also, tabular data often presents values for voltages of 220 volts and 380 volts. Plus, the installation conditions are taken into account - closed or open wiring. In fact, it turns out that one sheet of paper or a picture loaded into a smartphone contains voluminous technical information that allows you to do without the above-mentioned mathematical (linear) calculations.

Moreover, many manufacturers of cable products, in order to make it easier for the buyer to choose the right conductor, for example, for installing sockets, offer a table in which all the necessary values are entered. All that remains is to determine what load is planned for a specific electrical point and how the installation will be performed, and based on this information, select the correct wire with copper or aluminum conductors.

Which cable to choose for apartment wiring

Despite the cheapness of aluminum conductors, it is better to avoid using them. The reason is the low reliability of the contacts through which currents will pass. The second reason is the mismatch of the wire cross-section with the power of modern household appliances. Copper cable is reliable and has a long service life.

In apartments and houses it is allowed to use wire marked:

PUNP is a flat conductor with copper conductors in a PVC sheath. Designed for a nominal voltage of 250 V at a frequency of 50 Hz.
VVG/VVGng – flat cables made of copper with double PVC coating. They are used inside and outside buildings and are not subject to fire. They come with 2, 3 and 4 cores.
NYM - copper wire for internal single line. It has an insulating PVC sheath and outer covering, conductors with and without grounding.

When choosing the number of cores, you will need to take into account the conductivity per unit cross-section. In this case, it is better to make the apartment network from a single-core wire, the thickness of which is greater. Multicore elements can be bent many times and electrical appliances can be connected to them. Only a cable with thin cores will be of high quality.

The correct cross-section of conductors, taking into account the power of the equipment and the type of network are important factors when organizing an electrical line. The cable diameter can be calculated independently in several ways. Based on these readings, it is easy to determine the cross-section of the cores using formulas or using a table.

What is the cross section measured in?

After determining the diameter using the indicated methods, the cross-sectional area can be determined using a formula or a special table. It is measured in square millimeters. This unit of measurement is derived according to the Unified International System of Measurements.

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Unit of measurement

At the same time, the cut of the vein was always round.