AWG Wire Gauge Calculator — size, resistance and voltage drop

Convert AWG to mm², look up ampacity and resistance per metre, and pick a gauge for a given current and run length.

Example: AWG 14 copper carrying 10 A over 5 m drops 807.3 mV and wastes 8.073 W.

Inputs

AWG size

Smaller number means thicker wire.

Current(A)

Run length (one way)(m)

The calculation doubles this — current has to return.

Conductor

Supply voltage(V)

Optional — lets the drop be shown as a percentage.

Result

Voltage drop

807.3 mV

Drop as % of supply: 6.73%
Conductor diameter: 1.628 mm
Cross-section: 2.081 mm²
Resistance: 8.073 mΩ/m
Loop resistance: 80.73 mΩ
Power lost as heat: 8.073 W
Chassis wiring limit: 32 A
Power transmission limit: 5.9 A

6.7% drop is above the 3% usually treated as the practical limit. Go thicker, shorten the run, or raise the supply voltage.
10 A is above the 5.9 A power-transmission figure but below the 32 A chassis figure. Acceptable for a short run in free air; not for a long bundled run.
Ampacity figures are general guidance, not a code-compliant rating. Insulation temperature rating, bundling, conduit fill and ambient temperature all change the real limit — consult NEC, IEC 60364 or your local code for installed wiring.

Formula

d = 0.127 × 92^((36 − n)/39) mm    R = ρL / A

Worked example

AWG 14 copper carrying 10 A over 5 m drops 807.3 mV and wastes 8.073 W.

d = 0.127 × 92^((36 − n)/39) mm
d = 0.127 × 92^((36 − 14)/39)
d = 1.6277 mm
AWG is a geometric series — every 6 gauges roughly doubles the diameter.
R = ρ × L / A
R = 1.680e-8 × 10 / 2.081e-6
R = 80.73 mΩ
L is doubled because the current has to return.
V_drop = I × R
V_drop = 10 A × 80.73 mΩ
V_drop = 807.3 mV

Frequently asked questions

How many amps can 14 AWG wire carry?

Around 32 A for short chassis wiring in free air, but only about 5.9 A for long power-transmission runs. The gap is entirely about heat dissipation: a short wire in open air sheds heat easily, while a long bundled run in conduit does not. For installed wiring, follow your local electrical code rather than either figure.

Why does the calculation double my cable length?

Because current has to get back. A 5 m run means 10 m of conductor in the loop, and the drop happens along all of it. Halving the answer is the single most common mistake in voltage-drop calculations.

What is the 3% voltage drop rule?

A convention that the drop across a feeder run should stay under 3% of supply voltage, so the load actually sees close to its nominal voltage. It matters far more at low voltages — 0.36 V is 3% of 12 V but only 0.15% of 240 V, which is why 12 V systems need surprisingly thick cable.

How much worse is aluminium than copper?

About 58% more resistive for the same cross-section, so aluminium needs roughly two AWG sizes thicker to match copper. It is lighter and cheaper per amp, which is why utilities use it, but it also creeps under terminal screws and needs connectors rated for it.

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