AWG 28 wire size, resistance and weight calculator
AWG 28 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
- 0.321 094
- Area in circular mils
- 0.159 807
- Resistance of that length
- 21.2904 ohm
- Resistance per kilometre
- 212.904 ohm/km
- Resistance per 1000 feet
- 64.8931 ohm
- Weight of that length
- 0.072 554 1
- Current at the chosen density
- 0.32 A
- Turns per centimetre, close-wound
- 31.144
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 - (28)) / 39) = 0.321 094
- diameter_in = 0.321 094 / 25.4 = 0.012 641 5
- Cross-sectional area = pi * 0.321 094^2 / 4 = 0.080 975 5
- Area in circular mils = 0.012 641 5^2 * 1000 = 0.159 807
- r_per_m_20 = 1.724e-8 / (0.080 975 5 * 1e-6) = 0.212 904
- r_per_m = 0.212 904 * (1 + 0.00393 * (20 - 20)) = 0.212 904
- Resistance of that length = 0.212 904 * 100 = 21.2904
- Resistance per kilometre = 0.212 904 * 1000 = 212.904
- Resistance per 1000 feet = 0.212 904 * 304.8 = 64.8931
- Weight of that length = 0.080 975 5 * 1e-6 * 100 * 8960 = 0.072 554 1
- Current at the chosen density = 0.080 975 5 * 4 = 0.323 902
- Turns per centimetre, close-wound = 0.321 094 > 0 ? 10 / 0.321 094 : 0 = 31.1435
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 28 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.