AWG 38 wire size, resistance and weight calculator
AWG 38 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
- 0.100 716
- Area in circular mils
- 0.015 722 7
- Resistance of that length
- 216.398 ohm
- Resistance per kilometre
- 2163.98 ohm/km
- Resistance per 1000 feet
- 659.582 ohm
- Weight of that length
- 0.007 138 24
- Current at the chosen density
- 0.03 A
- Turns per centimetre, close-wound
- 99.290
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 - (38)) / 39) = 0.100 716
- diameter_in = 0.100 716 / 25.4 = 0.003 965 18
- Cross-sectional area = pi * 0.100 716^2 / 4 = 0.007 966 79
- Area in circular mils = 0.003 965 18^2 * 1000 = 0.015 722 7
- r_per_m_20 = 1.724e-8 / (0.007 966 79 * 1e-6) = 2.163 98
- r_per_m = 2.163 98 * (1 + 0.00393 * (20 - 20)) = 2.163 98
- Resistance of that length = 2.163 98 * 100 = 216.398
- Resistance per kilometre = 2.163 98 * 1000 = 2163.98
- Resistance per 1000 feet = 2.163 98 * 304.8 = 659.582
- Weight of that length = 0.007 966 79 * 1e-6 * 100 * 8960 = 0.007 138 24
- Current at the chosen density = 0.007 966 79 * 4 = 0.031 867 1
- Turns per centimetre, close-wound = 0.100 716 > 0 ? 10 / 0.100 716 : 0 = 99.2895
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 38 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.