AWG 4 wire size, resistance and weight calculator
AWG 4 is defined by the gauge formula, not by a table: the diameter is 0.127 mm times 92 raised to the power (36 - n) / 39. Everything else follows from that and the conductor resistivity.
A rough guide: 3 to 5 A/mm2 for chassis wiring, under 2 for long runs in conduit.
- Diameter
- 5.1894
- Area in circular mils
- 41.7413
- Resistance of that length
- 0.081 510 5 ohm
- Resistance per kilometre
- 0.815 105 ohm/km
- Resistance per 1000 feet
- 0.248 444 ohm
- Weight of that length
- 18.951
- Current at the chosen density
- 84.60 A
- Turns per centimetre, close-wound
- 1.927
Show the working
- Length of wire = 100
- Conductor = 1.724e-8
- Conductor temperature = 20
- Conductor density = 8960
- Design current density = 4
- Diameter = 0.127 * 92^((36 - (4)) / 39) = 5.1894
- diameter_in = 5.1894 / 25.4 = 0.204 307
- Cross-sectional area = pi * 5.1894^2 / 4 = 21.1506
- Area in circular mils = 0.204 307^2 * 1000 = 41.7413
- r_per_m_20 = 1.724e-8 / (21.1506 * 1e-6) = 0.000 815 105
- r_per_m = 0.000 815 105 * (1 + 0.00393 * (20 - 20)) = 0.000 815 105
- Resistance of that length = 0.000 815 105 * 100 = 0.081 510 5
- Resistance per kilometre = 0.000 815 105 * 1000 = 0.815 105
- Resistance per 1000 feet = 0.000 815 105 * 304.8 = 0.248 444
- Weight of that length = 21.1506 * 1e-6 * 100 * 8960 = 18.951
- Current at the chosen density = 21.1506 * 4 = 84.6026
- Turns per centimetre, close-wound = 5.1894 > 0 ? 10 / 5.1894 : 0 = 1.927 01
Values are shown to six significant figures here; the arithmetic itself runs on exact fractions and is only rounded where a number is printed.
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The formula
- diameter in mm = 0.127 x 92^((36 - n)/39)
- area = pi d^2 / 4
- resistance = rho x length / area
- temperature correction: R(T) = R(20) x (1 + 0.00393 (T - 20)) for copper
The gauge formula is exact: 36 AWG is 0.127 mm and 0000 AWG is 11.684 mm, with 39 steps between them in a geometric progression of ratio 92^(1/39).
The current figure is a design rule of thumb from current density, not an ampacity rating. Real ampacity depends on insulation temperature rating, bundling, ambient temperature and the wiring code in force.
Aluminium conductors of the same gauge carry about 61% of the current of copper for the same heating.
Frequently asked
What is the diameter of AWG 4 wire?
It follows from the gauge definition: 0.127 mm x 92^((36 - n)/39). The calculator shows the result in millimetres and inches.
Why does the wire gauge number go down as the wire gets thicker?
The number counts drawing operations. Each pass through a die makes the wire thinner and adds one to the gauge, so a high number means a thin wire.