12 V wire gauge at 3% voltage drop
Each cell is the smallest copper AWG size that carries the current and keeps the drop at or below 3% of 12 V, which is 0.36 V across the whole round trip. The charts use the voltage drop formula VD = 2 × 12.9 × I × L ÷ circular mils, and an ampacity floor from the NEC 75°C column (7 A for 18 AWG and 10 A for 16 AWG under 240.4(D)).
| Load | 5 ft | 10 ft | 15 ft | 20 ft | 25 ft | 30 ft | 40 ft | 50 ft |
|---|---|---|---|---|---|---|---|---|
| 5 A | 16 | 14 | 12 | 10 | 10 | 8 | 8 | 6 |
| 10 A | 14 | 10 | 8 | 8 | 6 | 6 | 4 | 4 |
| 15 A | 12 | 8 | 8 | 6 | 4 | 4 | 3 | 2 |
| 20 A | 10 | 8 | 6 | 4 | 4 | 3 | 2 | 1 |
| 30 A | 8 | 6 | 4 | 3 | 2 | 2 | 1/0 | 2/0 |
| 40 A | 8 | 4 | 3 | 2 | 1 | 1/0 | 2/0 | 3/0 |
| 50 A | 6 | 4 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 |
| 60 A | 6 | 3 | 2 | 1/0 | 2/0 | 2/0 | 4/0 | >4/0 |
| 80 A | 4 | 2 | 1/0 | 2/0 | 3/0 | 4/0 | >4/0 | >4/0 |
| 100 A | 3 | 1 | 2/0 | 3/0 | 4/0 | >4/0 | >4/0 | >4/0 |
Example: a 30 A load 20 ft away needs 3 AWG. A 10 A load 10 ft away needs 10 AWG, and a 5 A load 5 ft away only 16 AWG.
12 V at 10% drop (loads that tolerate it)
Some loads, such as pumps, fans and some lighting, tolerate more drop. If the equipment allows a lower voltage and you accept the lost power, the wire can be smaller. Check the equipment's minimum voltage first, because a loaded battery already sits below 12.6 V.
| Load | 5 ft | 10 ft | 15 ft | 20 ft | 25 ft | 30 ft | 40 ft | 50 ft |
|---|---|---|---|---|---|---|---|---|
| 5 A | 18 | 18 | 18 | 16 | 14 | 14 | 12 | 12 |
| 10 A | 16 | 16 | 14 | 12 | 12 | 12 | 10 | 8 |
| 15 A | 14 | 14 | 12 | 12 | 10 | 10 | 8 | 8 |
| 20 A | 12 | 12 | 12 | 10 | 8 | 8 | 6 | 6 |
| 30 A | 10 | 10 | 10 | 8 | 8 | 6 | 6 | 4 |
| 40 A | 8 | 8 | 8 | 6 | 6 | 6 | 4 | 3 |
| 50 A | 8 | 8 | 8 | 6 | 4 | 4 | 3 | 2 |
| 60 A | 6 | 6 | 6 | 6 | 4 | 4 | 3 | 2 |
| 80 A | 4 | 4 | 4 | 4 | 3 | 3 | 1 | 1/0 |
| 100 A | 3 | 3 | 3 | 3 | 2 | 2 | 1/0 | 2/0 |
24 V at 3% voltage drop
Doubling the voltage halves the current for the same watts and cuts the percentage drop by four for the same wire. That is why larger solar, RV and boat systems use 24 V or 48 V.
| Load | 5 ft | 10 ft | 15 ft | 20 ft | 25 ft | 30 ft | 40 ft | 50 ft |
|---|---|---|---|---|---|---|---|---|
| 5 A | 18 | 16 | 14 | 14 | 12 | 12 | 10 | 10 |
| 10 A | 16 | 14 | 12 | 10 | 10 | 8 | 8 | 6 |
| 15 A | 14 | 12 | 10 | 8 | 8 | 8 | 6 | 4 |
| 20 A | 12 | 10 | 8 | 8 | 6 | 6 | 4 | 4 |
| 30 A | 10 | 8 | 8 | 6 | 4 | 4 | 3 | 2 |
| 40 A | 8 | 8 | 6 | 4 | 4 | 3 | 2 | 1 |
| 50 A | 8 | 6 | 4 | 4 | 3 | 2 | 1 | 1/0 |
| 60 A | 6 | 6 | 4 | 3 | 2 | 2 | 1/0 | 2/0 |
| 80 A | 4 | 4 | 3 | 2 | 1 | 1/0 | 2/0 | 3/0 |
| 100 A | 3 | 3 | 2 | 1 | 1/0 | 2/0 | 3/0 | 4/0 |
How to size a 12 V wire
- Find the amps: watts ÷ 12. A 240 W load is 20 A (see the watts to amps chart).
- Measure the one-way distance from the power source to the load along the actual route.
- Read the size from the table, or step up one size for continuous loads, warm locations or a long bundle.
- Fuse the wire at its source, rated at or below the wire's ampacity.
Frequently asked questions
What gauge wire for 12V 20 amps?
8 AWG copper for runs up to about 11 ft at 3% drop, 6 AWG up to about 18 ft and 4 AWG up to about 29 ft. 12 AWG carries 20 A but drops too much voltage beyond about 4.5 ft.
What size wire for 12V 30 amps?
6 AWG for up to about 12 ft at 3% drop, and 4 AWG for up to about 19 ft.
How far can I run 12 gauge wire at 12 volts?
At 10 A, about 9 ft one way within 3% drop. At 5 A, about 18 ft. At 15 A, about 6 ft.
Is 3% voltage drop necessary?
The NEC recommends 3% for branch circuits, and 3% is a good target for electronics and lights. Check the minimum voltage your equipment accepts before allowing more.