DC wire gauge calculator

What gauge wire do you need?

Size 12V, 24V and 48V DC cable by current, run length and allowed voltage drop. The result is the thicker of what voltage drop and wire ampacity require.

System voltage

Current (amps)

Device watts ÷ voltage.

One-way length (ft)

Distance from source to device. We double it for the return wire.

Allowed voltage drop

Wire gauge—AWG

Voltage drop—

Suggested fuse—

Uses copper conductor and a conservative ampacity chart. Fuse as close to the battery as possible.

Gear that fits this result

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Why voltage drop matters on DC systems

Every foot of wire has a little resistance, and at low voltages that resistance eats a large share of your power. Lose 1 volt on a 120V house circuit and nobody notices. Lose 1 volt on a 12V circuit and you've lost over 8%, enough to make a fridge compressor struggle or a charger shut off.

Circular mils = (2 × 10.75 × Amps × One-way feet) ÷ Allowed volts of drop

10.75 is the resistance constant for copper. The 2 accounts for the round trip: current goes out on the positive wire and comes back on the negative. The result is a cross-section in circular mils, which maps to a wire gauge.

Worked example

A 20A load sits 10 feet from the battery on a 12V system, and you want no more than 3% drop (0.36V). (2 × 10.75 × 20 × 10) ÷ 0.36 = about 11,900 circular mils. 10 AWG is 10,380, which is too small, so you'd use 8 AWG at 16,510.

Ampacity: the second check

Short runs can pass the voltage-drop test with wire that's too thin to carry the current safely. A 150A inverter cable that's only 2 feet long might need just 6 AWG for voltage drop, but 6 AWG can't safely carry 150A. The calculator checks both and gives you the thicker answer.

AWG reference

Gauge (AWG)	Circular mils	Conservative max amps
14	4,110	20
12	6,530	25
10	10,380	35
8	16,510	50
6	26,240	65
4	41,740	85
2	66,360	115
1/0	105,600	150
2/0	133,100	175
4/0	211,600	230

Wire with higher-temperature insulation, run in free air, can be rated for more current than this table shows. Bundled wires and hot engine spaces are rated lower. When in doubt, go one size up.

Fuses protect the wire, not the device. Every positive wire needs a fuse or breaker sized at or below the wire's ampacity, placed as close to the battery as practical. Lithium banks feeding large inverters need a Class T fuse.

Frequently asked questions

What size wire for a 12V fridge?

Most 12V fridges draw 4–6A while running but are sensitive to voltage drop. For a 15-foot run, 10 or 12 AWG keeps drop under 3%. Enter your exact length above.

What gauge wire for a 2,000W inverter?

At 12V a 2,000W inverter can draw about 185A. With a short run, that usually means 2/0 or 3/0 AWG copper. Keep the cables as short as possible and fuse them close to the battery.

Is AWG the same as marine wire sizing?

Yes, marine wire uses AWG sizes. Good marine wire is fine-stranded and tinned to resist corrosion, which is also a smart choice for vans and RVs.

Should I size wire for 3% or 10% voltage drop?

Use 3% for anything sensitive or motor-driven, like pumps, fridges, chargers and electronics. 10% is the outer limit for non-critical loads like some lighting. We offer 3% and 5% to keep you on the safe side.