12V Wire Size Chart: Amps vs Length

At 12 V, short lengths need thick wire: 30 amps over 10 ft needs 6 AWG, 100 amps over 10 ft needs 2 AWG and 200 amps over 10 ft needs 3/0 AWG. Read your amps down the left and your one-way length across the top.

The answer

6 AWG copper

30 A, 10 ft one way, 12 V

Smallest copper wire at 12 V DC with a 3% voltage drop, by amps (rows) and one-way length (columns)
Amps 5 ft10 ft15 ft20 ft30 ft
10 A 14 AWG12 AWG10 AWG8 AWG6 AWG
20 A 12 AWG8 AWG6 AWG6 AWG4 AWG
30 A 10 AWG6 AWG4 AWG4 AWG2 AWG
50 A 8 AWG4 AWG3 AWG2 AWG1/0 AWG
100 A 3 AWG2 AWG1/0 AWG2/0 AWG4/0 AWG
150 A 1/0 AWG1/0 AWG2/0 AWG4/0 AWG300 kcmil
200 A 3/0 AWG3/0 AWG4/0 AWG250 kcmil500 kcmil

Calculate for your exact distance

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How to read the chart

Find your load in amps on the left, then follow the row across to your one-way length, which is the distance from the battery or bus bar to the load. The return wire is already counted. The cell shows the smallest copper size that keeps the voltage drop within 3% and carries the current, at 20 °C. Cells with a lower AWG number are thicker wire.

Why 12 V needs thick wire

A 3% drop is only 0.36 V at 12 V, so there is very little voltage to lose in the wire. A given current in a given length of wire loses the same volts whatever the system voltage, but 0.36 V is a tiny budget. Doubling the length or the current doubles the drop, which is why the sizes in the chart climb so fast.

Short runs are limited by ampacity

On very short runs the drop is small, and the wire size is set by how much current the wire can carry safely. Longer runs are set by voltage drop. Charging circuits and sensitive electronics do better with a 1–2% target, which needs a larger wire than the chart shows. Use the 12V wire size calculator to change the drop target.

Fuse close to the battery

Fit a fuse or breaker near the source, sized to protect the wire rather than only the load. Never use a wire whose ampacity is below the fuse rating. This chart uses NEC building-wire ampacity as a conservative guide: marine, automotive and RV standards have their own tables, and a hot engine bay or a tight bundle of cables calls for thicker wire.

How these sizes are worked out
  • Each size is the smallest copper or aluminum wire that meets two limits: the table ampacity for the breaker (NEC Table 310.16, with the NEC 240.4(D) small-conductor limits) and a 3% voltage drop. The larger of the two is shown.
  • The chart shows copper wire with the terminations assumed rated 75 °C.
  • Voltage drop uses conductor resistance only, with the wire at 20 °C. Reactance is ignored, which is accurate for short runs.
  • No ambient temperature or bundling derating is applied. Hot locations and conduits with many current-carrying conductors need larger wire.
  • This is general information, not a substitute for a licensed electrician or your local code. Read the disclaimer, or use the wire size calculator for your exact run.

This is general information based on NEC tables, not a permit or an installation plan. Local amendments, the equipment nameplate and an inspector decide what is acceptable. Read the disclaimer.

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