AWG 25 wire size, resistance and weight calculator
AWG 25 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
- 0.454 666
- Area in circular mils
- 0.320 419
- Resistance of that length
- 10.6185 ohm
- Resistance per kilometre
- 106.185 ohm/km
- Resistance per 1000 feet
- 32.3651 ohm
- Weight of that length
- 0.145 473
- Current at the chosen density
- 0.65 A
- Turns per centimetre, close-wound
- 21.994
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 - (25)) / 39) = 0.454 666
- diameter_in = 0.454 666 / 25.4 = 0.017 900 2
- Cross-sectional area = pi * 0.454 666^2 / 4 = 0.162 359
- Area in circular mils = 0.017 900 2^2 * 1000 = 0.320 419
- r_per_m_20 = 1.724e-8 / (0.162 359 * 1e-6) = 0.106 185
- r_per_m = 0.106 185 * (1 + 0.00393 * (20 - 20)) = 0.106 185
- Resistance of that length = 0.106 185 * 100 = 10.6185
- Resistance per kilometre = 0.106 185 * 1000 = 106.185
- Resistance per 1000 feet = 0.106 185 * 304.8 = 32.3651
- Weight of that length = 0.162 359 * 1e-6 * 100 * 8960 = 0.145 473
- Current at the chosen density = 0.162 359 * 4 = 0.649 434
- Turns per centimetre, close-wound = 0.454 666 > 0 ? 10 / 0.454 666 : 0 = 21.9942
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 25 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.