12V wire size chart (12V, 24V and 48V DC)
Find the wire gauge for any low-voltage DC circuit: read down to your load current, across to your one-way run length, and the cell gives the smallest copper conductor that stays inside the voltage-drop limit and still carries the current. Sizes are shown in AWG with the metric equivalent, and the chart prints cleanly on one page.
12 V DC wire size chart — AWG at 3% voltage drop
Copper conductors at 45 °C. Run lengths are one-way (feet); the return conductor is already included.
| Load | 5 ft | 10 ft | 15 ft | 20 ft | 25 ft | 30 ft | 40 ft | 50 ft | 75 ft | 100 ft |
|---|---|---|---|---|---|---|---|---|---|---|
| 5 A(60 W) | 17 AWG1 mm² | 14 AWG2.5 mm² | 14 AWG2.5 mm² | 12 AWG4 mm² | 12 AWG4 mm² | 10 AWG6 mm² | 8 AWG10 mm² | 8 AWG10 mm² | 6 AWG16 mm² | 6 AWG16 mm² |
| 10 A(120 W) | 14 AWG2.5 mm² | 12 AWG4 mm² | 10 AWG6 mm² | 8 AWG10 mm² | 8 AWG10 mm² | 8 AWG10 mm² | 6 AWG16 mm² | 6 AWG16 mm² | 4 AWG25 mm² | 2 AWG35 mm² |
| 15 A(180 W) | 14 AWG2.5 mm² | 10 AWG6 mm² | 8 AWG10 mm² | 8 AWG10 mm² | 6 AWG16 mm² | 6 AWG16 mm² | 4 AWG25 mm² | 4 AWG25 mm² | 1/0 AWG50 mm² | 1/0 AWG50 mm² |
| 20 A(240 W) | 12 AWG4 mm² | 8 AWG10 mm² | 8 AWG10 mm² | 6 AWG16 mm² | 6 AWG16 mm² | 4 AWG25 mm² | 2 AWG35 mm² | 2 AWG35 mm² | 1/0 AWG50 mm² | 2/0 AWG70 mm² |
| 25 A(300 W) | 12 AWG4 mm² | 8 AWG10 mm² | 6 AWG16 mm² | 6 AWG16 mm² | 4 AWG25 mm² | 4 AWG25 mm² | 2 AWG35 mm² | 1/0 AWG50 mm² | 2/0 AWG70 mm² | 3/0 AWG95 mm² |
| 30 A(360 W) | 10 AWG6 mm² | 8 AWG10 mm² | 6 AWG16 mm² | 4 AWG25 mm² | 4 AWG25 mm² | 2 AWG35 mm² | 1/0 AWG50 mm² | 1/0 AWG50 mm² | 3/0 AWG95 mm² | 4/0 AWG120 mm² |
| 40 A(480 W) | 8 AWG10 mm² | 6 AWG16 mm² | 4 AWG25 mm² | 2 AWG35 mm² | 2 AWG35 mm² | 1/0 AWG50 mm² | 2/0 AWG70 mm² | 2/0 AWG70 mm² | 4/0 AWG120 mm² | — |
| 50 A(600 W) | 8 AWG10 mm² | 6 AWG16 mm² | 4 AWG25 mm² | 2 AWG35 mm² | 1/0 AWG50 mm² | 1/0 AWG50 mm² | 2/0 AWG70 mm² | 3/0 AWG95 mm² | 4/0 AWG120 mm² | — |
| 60 A(720 W) | 6 AWG16 mm² | 4 AWG25 mm² | 2 AWG35 mm² | 1/0 AWG50 mm² | 1/0 AWG50 mm² | 2/0 AWG70 mm² | 3/0 AWG95 mm² | 4/0 AWG120 mm² | — | — |
| 80 A(960 W) | 4 AWG25 mm² | 2 AWG35 mm² | 1/0 AWG50 mm² | 2/0 AWG70 mm² | 2/0 AWG70 mm² | 3/0 AWG95 mm² | 4/0 AWG120 mm² | — | — | — |
| 100 A(1200 W) | 2 AWG35 mm² | 2 AWG35 mm² | 1/0 AWG50 mm² | 2/0 AWG70 mm² | 3/0 AWG95 mm² | 4/0 AWG120 mm² | — | — | — | — |
| 125 A(1500 W) | 1/0 AWG50 mm² | 1/0 AWG50 mm² | 2/0 AWG70 mm² | 3/0 AWG95 mm² | 4/0 AWG120 mm² | 4/0 AWG120 mm² | — | — | — | — |
| 150 A(1800 W) | 1/0 AWG50 mm² | 1/0 AWG50 mm² | 3/0 AWG95 mm² | 4/0 AWG120 mm² | 4/0 AWG120 mm² | — | — | — | — | — |
| 200 A(2400 W) | 3/0 AWG95 mm² | 3/0 AWG95 mm² | 4/0 AWG120 mm² | — | — | — | — | — | — | — |
A dash means the load is beyond 4/0 AWG at that distance — split the circuit, move the load closer, or step up to a higher system voltage. Sizes are a design guide, not a substitute for NEC, ABYC or your local wiring rules.
How to use the amps vs wire size chart
- 1. Work out the load current: amps = watts ÷ system voltage. A 300 W 12 V inverter load draws 25 A.
- 2. Measure the one-way distance from the battery or fuse block to the load, following the cable route.
- 3. Pick the drop limit: 3% for lighting, electronics and charging circuits, 10% only for short high-current feeds where the manufacturer allows it.
- 4. Read the cell where the two meet — that is the minimum copper size. Round up if the run may get longer.
- 5. Fuse the cable, not the load: the overcurrent device must protect the conductor you actually install.
The formula behind it
area (mm²) = 2 × ρ × length (m) × amps ÷ allowed volt drop
ρ is copper resistivity, 0.0189 Ω·mm²/m at 45 °C. The 2 accounts for the positive and negative conductors. Allowed volt drop is the percentage of system voltage — 0.36 V at 12 V and 3%. The chart then checks the chosen size can also carry the current continuously and steps up if it cannot.
12V wire size questions
What size wire do I need for 12V?
It depends on amps and distance, not just amps. A 20 A load over a 10 ft one-way run needs 8 AWG at 12 V for a 3% drop, and the same 20 A over 30 ft needs 4 AWG because voltage drop, not heating, decides the size on 12 V systems.
How do I read an amps vs wire size chart for a 12 volt system?
Choose the load current in amps, then the one-way cable length. The chart gives the minimum copper AWG and mm² size that stays within the selected voltage-drop limit and also carries the current.
Can I use this chart as a 48V wire size chart?
Yes. Select 48 V at the top of the chart. Because the allowable voltage drop is higher at 48 V, the same power and distance often needs a smaller conductor than a 12 V circuit.
Why does 12V need such thick wire?
A 3% drop is only 0.36 V at 12 V, against 1.44 V at 48 V and 7 V at 230 V. The lower the system voltage, the less drop you can afford, so the same power needs far more copper.
Is the run length one way or round trip?
The lengths in this chart are one-way, from the battery or fuse block to the load. The calculation already doubles it for the return conductor.
What voltage drop is acceptable on a 12V system?
3% is the normal target for lighting, electronics and critical circuits; 5% or 10% is sometimes accepted for non-critical loads such as a winch or a starter feed on marine installations (ABYC allows 10% there).
Does this chart work for RV and marine wiring?
Yes — the physics is the same. For boats use tinned marine-grade stranded cable and check ABYC ampacity for engine spaces; for an RV, add margin where the cable runs through a hot chassis area.
Can I use these sizes for aluminium wire?
No. Aluminium has about 1.64x the resistance of copper, so go up roughly two AWG sizes, or use the DC cable size calculator with aluminium selected.
How is the wire size calculated?
Required area in mm² = 2 x ρ x length x amps ÷ allowed volt drop, with ρ = 0.0189 Ω·mm²/m for copper at 45 °C. The chart then picks the smallest standard conductor that also carries the current.