AWG 20 wire size, resistance and weight calculator
AWG 20 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
- 0.811 821
- Area in circular mils
- 1.021 53
- Resistance of that length
- 3.330 63 ohm
- Resistance per kilometre
- 33.3063 ohm/km
- Resistance per 1000 feet
- 10.1518 ohm
- Weight of that length
- 0.463 787
- Current at the chosen density
- 2.07 A
- Turns per centimetre, close-wound
- 12.318
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 - (20)) / 39) = 0.811 821
- diameter_in = 0.811 821 / 25.4 = 0.031 961 5
- Cross-sectional area = pi * 0.811 821^2 / 4 = 0.517 619
- Area in circular mils = 0.031 961 5^2 * 1000 = 1.021 53
- r_per_m_20 = 1.724e-8 / (0.517 619 * 1e-6) = 0.033 306 3
- r_per_m = 0.033 306 3 * (1 + 0.00393 * (20 - 20)) = 0.033 306 3
- Resistance of that length = 0.033 306 3 * 100 = 3.330 63
- Resistance per kilometre = 0.033 306 3 * 1000 = 33.3063
- Resistance per 1000 feet = 0.033 306 3 * 304.8 = 10.1518
- Weight of that length = 0.517 619 * 1e-6 * 100 * 8960 = 0.463 787
- Current at the chosen density = 0.517 619 * 4 = 2.070 48
- Turns per centimetre, close-wound = 0.811 821 > 0 ? 10 / 0.811 821 : 0 = 12.318
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 20 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.