A DC wire size calculator answers one question: what conductor must carry this DC current safely, over this distance, at this voltage? The answer has two parts, and the DC version of each is simpler than the AC version.
The maximum current a conductor can carry continuously before its insulation overheats. Same AWG chart for DC and AC — thermal limit doesn't care about alternation.
Voltage lost due to resistance. DC has no power factor or reactance — pure resistance × round-trip path. Simple, but unforgiving.
The result — the AWG number or mm² cross-section you order. A 30 A circuit needs 10 AWG for a short run; at 12 V over 5 m it forces 16 mm² (≈5 AWG).
A 30 A circuit needs 10 AWG copper by ampacity alone. Run that same 30 A at 12 V over 5 m and the DC drop forces 16 mm² (≈5 AWG), because 3% of 12 V is only 0.36 V. DC sizing is almost always voltage-drop sizing.
12v, 24v, and 48v wire size calculator in one tool.
Enter an inverter's wattage directly to get full-load DC amps.
Shows the formula, reports drop in both volts and percent.
Returns AWG and mm², plus fuse sizing — the steps most guides forget.
Size DC conductors for battery, solar, and marine circuits. Enter your voltage, current, and run length. The calculator returns AWG, mm², voltage drop, and fuse sizing.
Select a voltage preset or enter a custom voltage. The calculator applies the 2× round-trip DC voltage drop formula.
The most common DC sizing questions in the field. Use these charts as a quick reference for battery-to-inverter, solar, marine, and generator start circuits. For exact sizing, run the DC wire size calculator above with your specific voltage, current, and run length.
| Inverter (12 V) | Full-Load Current | Cable (1–2 m run) | Fuse |
|---|---|---|---|
| 400 W | 33 A | 6 AWG | 40 A |
| 750 W | 63 A | 4 AWG | 80 A |
| 1,000 W | 83 A | 2 AWG | 150 A |
| 1,500 W | 125 A | 1/0 AWG | 200 A |
| 2,000 W | 167 A | 2/0 AWG | 250 A |
| 3,000 W | 250 A | 4/0 AWG | 400 A |
CCA carries about 40% more resistance than pure copper, so it needs roughly two AWG sizes up to match copper's drop. Its connections can oxidize and heat under load. For battery, inverter, and solar runs, use pure copper — tinned marine-grade copper in wet or salt environments.
The tool works in four DC modes, so it serves a solar installer, a marine electrician, an off-grid van builder, and a generator buyer without any of them fighting the interface.
At 3% drop: 12V loses 0.36V, 24V loses 0.72V, 48V loses 1.44V. Higher voltage = lower current = smaller cable. Use 12V for automotive/RV/marine, 24V for telecom/trucks, 48V for solar & EV.
Enter inverter wattage — returns full-load DC current, cable, and fuse. Size on low-voltage cutoff (e.g. 10.5V for 12V), not nominal voltage. Fuse within 18 inches of the battery. Negative leg same as positive.
NEC 690: size conductors at 125% of Isc. A 10A panel → 12.5A design current. DC drop budget: 2% (tighter than the general 3%). The size is almost always voltage-drop limited.
ABYC E-11: 3% on critical circuits (bilge, nav, electronics), 10% on non-critical. Marine cable = tinned stranded copper, 105°C insulation. Automotive = SAE tables, thinner insulation, not for engine compartments.
Enter 36V, 72V, or any pack voltage. The calculator applies the same formula — only the drop budget changes. Higher voltage always means smaller cable for the same power.
A Class T or ANL fuse protects the short run where a short circuit is most likely. Size it at or below the cable ampacity for continuous duty, or to the inverter surge current where the cable is upsized. The negative leg must be the same size as the positive — it carries the same current and the same round-trip drop.
The DC voltage drop formula is Vd = 2 × L × I × R ÷ 1,000, where L is the one-way length in metres, I is the current in amps, R is the conductor resistance in Ω/km, and 2 accounts for the round trip. The drop as a percent is Vd ÷ V × 100, and it drives every DC sizing decision.
A 30A fridge on 12V, run 5m. 3% budget = 0.36V. 16 mm² drops 2.9% — OK. 10 mm² drops 4.6% — over. Answer: 16 mm² (≈5 AWG). Ampacity alone would allow 10 AWG, but voltage drop wins.
A 2,400W inverter on 24V draws 100A over 2m. 100A needs 2 AWG (115A at 75°C). Drop is 0.9%. Ampacity wins. If continuous, apply 125% → step to 1 AWG.
A 10A Isc panel → 12.5A design current (125% of Isc). Run 15m, 2% budget = 0.96V. 10 mm² drops 1.4% — OK. 6 mm² drops 2.4% — over. Answer: 10 mm² (≈7 AWG).
Recommended limits: 3% on a branch circuit, 5% total from source to load, and 2% for solar DC runs. This page doubles as a DC voltage drop calculator: the same formula returns the size, the volts dropped, and the percent remaining in one pass. Ampacity first, voltage drop second — and the bigger conductor wins.
If you have sized AC wire before, the DC difference is smaller than you might think, and it lives entirely in the voltage-drop step. Ampacity is identical; the budget is what bites.
The same Table 310.16 chart sizes a 12V DC circuit and a 240V AC circuit. The conductor's thermal limit doesn't know the difference.
DC uses the same 2× round-trip rule as single-phase AC. What DC does not add is power factor and reactance — pure resistance only.
A 240V AC circuit spends its 3% budget over 7.2V; a 12V DC circuit spends the same 3% over 0.36V. The same amps and metres that need 10 AWG at 240V need 4 AWG or larger at 12V.
Three-phase AC replaces the 2× round-trip with √3 (1.732). It drops about 13% less than single-phase on the same conductor, current, and distance.
For single- and three-phase AC sizing with power factor and the √3 rules, use the AC wire size calculator. This page is the DC side of that pair. Both feed the general wire size calculator, which returns DC and AC answers in both AWG and mm² in one pass.
Our engineers will review your DC circuit sizing, confirm the voltage drop, and deliver a factory-direct price — no obligation, no hidden fees. Every quote includes the cable, fuse, and battery package for your 12V, 24V, or 48V system, plus the generator behind the start battery.
A: It depends on the current and the run. For a 1,000 W inverter on a 12 V battery, the run draws about 83 A and needs 2 AWG copper over a short 1 to 2 metre run. For a light load like a 10 A fan over 5 metres, 8 AWG holds the drop at about 1.8%. Enter your amps and metres in the DC wire size calculator for the exact size, and don’t undersize the battery-to-inverter leg.
A: At 12 V and a 3% drop, 10 AWG carries about 5 A over a 10-metre run, or about 1.8 metres at 30 A. It’s a light-duty conductor at 12 V: the low voltage eats its distance budget fast. For 30 A at 12 V you need 16 mm² (about 5 AWG) over 5 metres, and 2 AWG over 10 metres.
A: At 12 V, a 2,000 W inverter draws about 167 A, so the battery run needs 2/0 AWG copper and a 250 A fuse. At 24 V the current drops to about 83 A, so 2 AWG covers it. At 48 V it drops to about 42 A, so 6 AWG is enough. Voltage is the cheapest upgrade in DC design: doubling it roughly halves the cable cost.
A: Only for low-current, short, fixed runs. CCA carries about 40% more resistance than copper, so it needs roughly two AWG sizes up to match copper’s drop, and its connections can oxidize and heat under load. For battery, inverter, and solar runs, use pure copper, tinned marine-grade copper in wet or salt environments.
A: Because the drop budget scales with the voltage. 3% of 12 V is 0.36 V; 3% of 120 V is 3.6 V. The 120 V circuit can lose ten times as many volts before the load complains, so the same amps and distance need a much smaller conductor. That’s why low-voltage DC runs look oversized next to their AC equivalents, and why raising the system voltage is the standard fix.
A: The formula is set out in the How to Calculate section above: Vd = 2 × L × I × R ÷ 1,000, with L in metres, I in amps, R in Ω/km, and the 2 covering the round trip. Divide by the system voltage for the percent drop, and keep it at or under 3% for branches and 2% for solar DC.
A: Yes, always. Install a Class T or ANL fuse within 18 inches of the battery, rated at or below the cable ampacity and about 125% of the full-load current. The battery can deliver hundreds of amps into a short circuit, and the fuse is the only thing that stops a cable fire before it starts.
A: Marine wire is tinned stranded copper with 105 °C insulation, built to survive salt air and constant vibration; automotive primary wire has thinner, lower-temperature insulation and won’t survive wet or battery-to-inverter duty. ABYC E-11 permits 3% drop on critical marine circuits and 10% on non-critical, while automotive sizing follows SAE ampacity tables and runs shorter and hotter.
