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Wire Gauge (AWG) Calculator

Look up AWG wire sizes 4/0 to 40 — diameter, cross-section and ohms per 1000 ft — and calculate voltage drop for copper or aluminium runs.

2.588 mm
Diameter
0.1019
Diameter (in)
5.261 mm²
Area
10.38
Area (kcmil)
0.9988 Ω
Resistance / 1000 ft
3.2768 Ω
Resistance / km

Voltage drop for a cable run

0.749 V
One-way drop
1.498 V
Round-trip drop
1.25%
Drop (% of supply)
118.5 V
Voltage at load

Notes

Vdrop = I × R × length, doubled for the round trip (out and back). Resistance uses copper at 20 °C; it rises roughly 0.4% per °C for copper, and real circuits should also respect code ampacity limits — treat this as an engineering estimate. A common guideline is to keep the drop under 3%.

What is the Wire Gauge (AWG) Calculator?

The ByteTools Wire Gauge Calculator covers the full American Wire Gauge range from AWG 4/0 down to AWG 40.

  • Full AWG table from 4/0 (0000) to 40
  • Diameter, area and resistance in metric and imperial units
  • Copper and aluminium at standard 20 °C resistivity
  • One-way and round-trip voltage drop with percentage
  • Feet or metres for run length
  • 100% private — runs entirely in your browser

How to use the Wire Gauge (AWG) Calculator

  1. 1

    Select a wire gauge from AWG 4/0 to 40 and a material (copper or aluminium).

  2. 2

    Read the diameter, cross-section and resistance per 1000 ft / km.

  3. 3

    Enter current, one-way run length and supply voltage.

  4. 4

    Read the one-way and round-trip voltage drop and percentage drop.

  5. 5

    Try neighbouring gauges to find the size that keeps drop under your target.

About the Wire Gauge (AWG) Calculator

The ByteTools Wire Gauge Calculator covers the full American Wire Gauge range from AWG 4/0 down to AWG 40. Pick a gauge to see its diameter in millimetres and inches, cross-sectional area in mm² and kcmil, and resistance per 1000 feet and per kilometre for copper or aluminium conductors at 20 °C.

It then computes voltage drop for a real cable run: enter the load current, one-way length and supply voltage, and read the one-way and round-trip drop in volts and as a percentage. Resistivity constants used are 1.724×10⁻⁸ Ω·m for annealed copper and 2.65×10⁻⁸ Ω·m for aluminium, the standard 20 °C reference values.

Note that resistance rises with temperature and ampacity depends on insulation and installation, so treat results as engineering estimates and consult your electrical code for safety-critical sizing. Everything runs 100% locally in your browser with nothing uploaded.

Frequently asked questions

How is AWG wire diameter calculated?

AWG is a geometric series: diameter in inches = 0.005 × 92^((36 − n) ÷ 39), where n is the gauge number (4/0 counts as −3). Each step down three gauge numbers roughly doubles the cross-sectional area, and AWG 10 works out to about 2.59 mm (0.1019 in).

How do I calculate voltage drop in a wire?

Multiply the wire's resistance per unit length by the run length and the current: Vdrop = I × R. For a circuit, use the round trip (out and back), which doubles the length. AWG 10 copper is about 0.999 Ω per 1000 ft, so 20 A over a 50 ft round-trip run drops roughly 2 V.

What percentage voltage drop is acceptable?

A common design guideline is to keep voltage drop under about 3% for branch circuits and 5% total including feeders. Low-voltage systems (12 V solar, automotive) are far more sensitive — 3% of 12 V is only 0.36 V — so they often need surprisingly thick wire.

Is aluminium wire worse than copper?

Aluminium has about 1.54× the resistivity of copper (2.65 vs 1.724 ×10⁻⁸ Ω·m at 20 °C), so an aluminium conductor needs roughly two gauge sizes larger for the same resistance. It is lighter and cheaper, which is why it dominates overhead power lines.

Does this tool tell me the safe ampacity of a wire?

No — it reports resistance and voltage drop only. Safe current-carrying capacity depends on insulation temperature rating, bundling, ambient temperature and the applicable electrical code (e.g. NEC tables), so always confirm ampacity against your local code.

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