AWG Wire Gauge & Ampacity Calculator
Enter your current draw and run length to find the minimum safe wire gauge — with voltage drop and power loss calculated in your browser. Works for 12 V van builds, marine wiring, and household AC. Nothing uploaded.
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| Gauge | mm² | Ampacity (A) | V-drop | Amp OK |
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Learn more: wire sizing, ampacity, and FAQ
Why undersized wire is dangerous
Every wire has resistance proportional to length and inversely proportional to cross-sectional area. When too much current flows through too thin a wire, the wire heats up. In a van, boat, or off-grid solar install, this can mean a fire inside a wall cavity with no easy escape route.
How to read AWG vs mm² wire sizes
AWG (American Wire Gauge) is the US standard where a lower number means a thicker wire - so 10 AWG is thicker than 12 AWG. mm² is the metric cross-sectional area standard used in Europe and most of the world. This calculator shows both side by side so you can order the right wire regardless of where you are buying it. A 10 AWG copper wire is roughly equivalent to 6 mm².
Voltage drop and why it matters
Wire resistance causes voltage to drop across the run. For sensitive electronics you want voltage drop under 2%; for lighting and general loads under 3% is acceptable. A 3% drop on a 12V circuit means the device at the end receives only 11.64V. Longer runs always need heavier wire to stay within safe limits.
DC vs AC voltage systems
This calculator covers DC systems (12V, 24V, 48V used in van builds, boats, and solar), and mains AC (120V in North America, 230V in Europe and most of the world). The voltage drop formula and ampacity ratings differ between DC and AC, but the principle remains the same - match wire size to current, run length, and acceptable voltage loss.
FAQ
What wire gauge do I need for a 20A 12V circuit?
For a 20A draw over a 3-metre one-way run (6m round trip), a minimum of 10 AWG (6mm²) copper is recommended to keep voltage drop under 3%. The exact answer depends on your specific run length - enter your values into the calculator for a precise result.
Why does run length matter for wire sizing?
Wire resistance accumulates with length. A 1-metre cable drops far less voltage than a 10-metre cable carrying the same current. For sensitive electronics you want voltage drop under 2%; for lighting and general loads under 3% is acceptable. Longer runs always need heavier wire.
What is the difference between AWG and mm²?
AWG (American Wire Gauge) is the US standard where a lower number means a thicker wire. mm² is the metric cross-sectional area standard used in Europe and most of the world. The calculator shows both side by side so you can order the right wire wherever you are buying it.