AWG Wire Size Calculator
Exact diameter, area, resistance and rule-of-thumb ampacity for any AWG gauge — from the ASTM B258 formula, not a lookup.
The two ampacity figures are rules of thumb for hookup wire in electronics. Insulation temperature rating, bundling and ambient change everything: NEC 310.16 (building wire in conduit) allows e.g. 30 A on 10 AWG @ 60 °C insulation, while a free-air 10 AWG chassis lead handles far more. For mains wiring, the electrical code of your country is the law — not this page.
AWG Wire Size Calculator computes the exact diameter, cross-section, resistance and rule-of-thumb ampacity of any AWG gauge — free, instant and private in your browser. Makers buying hookup wire, harness designers and anyone translating AWG ↔ mm² use it to skip the datasheet algebra: type your numbers, read the answer with the substituted formula shown step by step, and share an exact permalink of the calculation.
About AWG Wire Size Calculator
AWG Wire Size Calculator computes the exact diameter, cross-section, resistance and rule-of-thumb ampacity of any AWG gauge using the standard engineering relation: d(mm) = 0.127·92^((36−n)/39) (ASTM B258), then R = ρ/A and I ≈ CM/700…CM/300. Worked live: AWG 18 is 1.02 mm diameter, ~21 Ω/km, good for ~2.3 A on long runs or ~5 A in short chassis hops. The result recalculates on every keystroke, the worked-example panel shows your numbers substituted into the formula, and the Copy permalink button encodes the inputs in the URL so a colleague opens exactly your calculation. Everything runs client-side — nothing you type leaves your device.
How to use AWG Wire Size Calculator
- 1Enter your values — the tool starts with realistic defaults for this exact use case, so the worked example is meaningful immediately.
- 2Read the live result and the worked-example panel, which substitutes your numbers into the formula step by step.
- 3Adjust any input to compare scenarios, then use Copy result or Copy permalink to share the calculation.
Why use AWG Wire Size Calculator?
- ✓Implements the real formula — d(mm) = 0.127·92^((36−n)/39) (ASTM B258), then R = ρ/A and I ≈ CM/700…CM/300 — with the substitution shown, not a black box
- ✓Built for makers buying hookup wire, harness designers and anyone translating AWG ↔ mm²
- ✓Copy result and permalink buttons — share the exact calculation in a README, forum answer or design review
- ✓100% free, no sign-up, runs entirely in your browser (works offline once loaded)
Frequently asked questions
How do you calculate awg wire size?+
The exact diameter, cross-section, resistance and rule-of-thumb ampacity of any AWG gauge follows d(mm) = 0.127·92^((36−n)/39) (ASTM B258), then R = ρ/A and I ≈ CM/700…CM/300. For example, AWG 18 is 1.02 mm diameter, ~21 Ω/km, good for ~2.3 A on long runs or ~5 A in short chassis hops. The calculator applies the same relation and shows the substituted arithmetic so you can verify every step.
Why do AWG numbers get smaller as wire gets bigger?+
The number counts drawing-die steps from the original rod — more draws, thinner wire. Handy mental math: −3 AWG doubles the cross-section, −6 AWG doubles the diameter, +10 AWG is 10× the resistance.
Which ampacity figure should I trust — they vary everywhere?+
Because ampacity is thermal, not electrical: insulation rating, bundling and ambient set it. The CM/700 'power transmission' rule is conservative for bundles and long runs; CM/300 suits short free-air chassis wires; building wiring must follow your electrical code's tables, full stop.
Is the AWG Wire Size Calculator free and private?+
Yes — completely free with no sign-up or usage limits, and it runs entirely in your browser: the values you enter are never uploaded or stored on a server.
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