12 Volt Wire Size Chart
Minimum copper cable size (AWG) by current and one-way distance, at 3% voltage drop.
| Current | 3 ftone way | 5 ftone way | 10 ftone way | 15 ftone way | 20 ftone way | 25 ftone way |
|---|---|---|---|---|---|---|
| 5 A | 16 | 16 | 14 | 12 | 12 | 10 |
| 10 A | 16 | 14 | 12 | 10 | 8 | 8 |
| 15 A | 14 | 12 | 10 | 8 | 6 | 6 |
| 20 A | 14 | 12 | 8 | 6 | 6 | 4 |
| 30 A | 12 | 10 | 6 | 4 | 4 | 2 |
| 40 A | 10 | 8 | 6 | 4 | 2 | 2 |
| 50 A | 10 | 8 | 4 | 2 | 2 | 1/0 |
| 60 A | 10 | 6 | 4 | 2 | 1/0 | 1/0 |
| 80 A | 8 | 6 | 2 | 1/0 | 1/0 | 2/0 |
| 100 A | 6 | 4 | 2 | 1/0 | 2/0 | 3/0 |
| 125 A | 4 | 4 | 1/0 | 2/0 | 3/0 | 4/0 |
| 150 A | 4 | 2 | 1/0 | 3/0 | 4/0 | — |
| 200 A | 2 | 2 | 2/0 | 4/0 | — | — |
| 250 A | 1/0 | 1/0 | 3/0 | — | — | — |
| 300 A | 2/0 | 2/0 | 4/0 | — | — | — |
Sizes are for copper cable on a 12-volt circuit. — means no single cable up to 4/0 will do: shorten the run, use a higher voltage, or run two cables in parallel.
How to read the chart
- Find your currentAmps = watts ÷ volts. For an inverter, use its watts ÷ 10, which allows for the inverter’s losses.
- Measure one wayUse the distance from the battery to the load, not the round trip — the chart already allows for the return wire.
- Round upIf you fall between rows or columns, use the higher current and the longer distance. A smaller AWG number means a thicker cable.
Good to know
- Two limits, one answer. Each size keeps voltage drop to 3% and is at least what the cable is rated to carry (ABYC figures for 105°C-rated cable outside engine spaces). On short, high-current runs it is the current rating that decides.
- Hot or crowded spaces. In an engine compartment, or bundled with other cables, go one size thicker.
- 3% or 10%? 3% suits inverters, electronics, pumps and motors. Lighting can tolerate up to 10% — the inverter calculator works out any voltage drop.
- Fuse the positive cable as close to the battery as you can, sized to protect the cable. See Class T fuses compared.