Solar Wire Size Calculator

Find the right AWG wire gauge for your solar system. Covers DC and AC circuits with a full comparison table showing voltage drop and power loss for every gauge.

Circuit parameters

Current?

One-way distance?

System voltage?

Max voltage drop?

Recommended wire gauge

AWG 12

Voltage drop0.95V (3.97%)

Power loss19.1 W

Max allowed drop0.72V (3%)

Status✗ Exceeds limit

AWG comparison table

AWG	Ampacity	Drop V	Drop %	Loss W
14	15A	1.52V	6.31%	30.3W
► 12	20A	0.95V	3.97%	19.1W
10	30A	0.60V	2.50%	12.0W
8	40A	0.38V	1.57%	7.5W
6	55A	0.24V	0.99%	4.7W
4	70A	0.15V	0.62%	3.0W
2	95A	0.09V	0.39%	1.9W
1	110A	0.07V	0.31%	1.5W
1/0	125A	0.06V	0.25%	1.2W
2/0	145A	0.05V	0.19%	0.9W
3/0	165A	0.04V	0.15%	0.7W
4/0	195A	0.03V	0.12%	0.6W

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How to Use This Calculator

Enter the current in amps

Use the actual current that will flow through the wire. For solar applications: panel-to-controller runs use panel Isc × 1.25 (NEC 125% safety factor). Battery-to-inverter cables use inverter rated watts ÷ battery voltage. For branch circuits, use the load's rated current × 1.25.

Enter the one-way distance

Measure the one-way distance from source to load. The calculator automatically doubles this to account for both the positive and negative conductors (the return path). In a 24V system, the negative cable carries the same current as the positive — both must be sized correctly.

Set system voltage and max voltage drop

Lower voltages are more sensitive to voltage drop. A 1V drop on a 12V system is 8.3% — on a 240V system it's 0.4%. The NEC recommends 3% maximum for branch circuits. For solar systems, use 1-2% for critical runs (battery bank to inverter, high-current DC runs) and up to 5% for less critical runs (panel combiner to charge controller).

Read the AWG table

The results table shows every AWG size, its ampacity rating, calculated voltage drop, and power loss for your specific circuit. The recommended wire is highlighted. Going one size larger than the minimum is inexpensive and reduces power loss noticeably — worth considering for permanent installations.

The Formula

Total wire length = One-way distance × 2 (round trip) Max resistance = (System voltage × Max drop %) ÷ Current Required resistivity ≤ Max resistance × 1,000 ÷ Total length (in ohms/1,000ft) Actual voltage drop = Current × (Wire resistance/1,000ft × Total length / 1,000) Actual drop % = Voltage drop ÷ System voltage × 100 Power loss = Voltage drop × Current

Copper resistivity values (ohms per 1,000 feet at 75°C) come from standard AWG tables. The calculator uses NEC Table 9 values for stranded copper conductors — the same table electricians use for code compliance.

Quick AWG Reference

AWG 1415A max — lighting, small loads

AWG 1220A max — standard branch circuits

AWG 1030A max — dryers, EV charging (NEMA 14-30)

AWG 840A max — ranges, large AC units

AWG 655A max — solar panel combiner runs

AWG 470A max — charge controller output at 24V

AWG 295A max — battery bank connections

AWG 1/0125A max — large inverter DC cables

AWG 2/0145A max — heavy inverter/battery connections

AWG 4/0195A max — high-capacity battery banks

Example

Battery to inverter cable — 24V, 2,000W system

A 2,000W inverter on a 24V battery bank draws up to 2,000 ÷ 24 = 83A DC. The inverter is 8 feet from the battery bank (one-way).

Current83 A

One-way distance8 ft

Total wire length16 ft

System voltage24V

Max drop target2% = 0.48V

Max resistance allowed0.48 ÷ 83 = 0.00578 Ω

Recommended wireAWG 2/0 (0.078 Ω/1,000ft)

Actual voltage drop0.10V (0.43%)

AWG 2/0 handles the 83A load within the 2% drop target for a short 8-foot run. Using AWG 1/0 (125A rated) would give 0.13V drop at 0.54% — slightly over the 2% target but still below 3%. For this critical high-current run, AWG 2/0 is the right choice — the cost difference is minimal but the efficiency gain is real.

FAQ

What voltage drop percentage should I use for solar systems? ▼

Use 1-2% for critical high-current DC runs (battery to inverter, battery to load center). These runs are permanently at high current and losses directly reduce system efficiency. Use 2-3% for panel-to-controller runs and controller-to-battery runs. Use 3-5% for AC branch circuits where voltage drop is less critical. The NEC's 3% recommendation was designed for 120V AC systems — the same absolute voltage drop is proportionally much larger on 12V or 24V DC systems, so tighter limits are appropriate.

Does wire gauge matter for short runs? ▼

Yes — for high-current DC circuits (battery bank connections, inverter cables), even short runs matter. The resistance is proportional to length, but the current is so high that even 2 feet of undersized wire creates measurable voltage drop and heat. Battery bank interconnect cables, battery-to-inverter cables, and ground cables should all be sized for minimal voltage drop regardless of distance. Use the calculator with your actual short distance — the table will show you the exact trade-off.

Can I use aluminum wire for solar systems? ▼

Aluminum wire is used in utility-scale solar and large commercial installations to reduce cost and weight. For residential solar wiring (panel wiring, DC circuits), copper is standard because aluminum requires special lugs, connections are more failure-prone over time, and the wire must be 2 AWG sizes larger for equivalent current capacity. Aluminum is appropriate for service entrance conductors and large feeder runs but not for solar panel wiring or battery connections. This calculator uses copper values.

What is ampacity and why does it matter? ▼

Ampacity is the maximum current a wire can carry without overheating and degrading its insulation. It's determined by conductor size, insulation temperature rating, and installation method (conduit, free air, buried). Undersized wire overheats, melts insulation, and can cause fires — even if the voltage drop is acceptable. Always ensure your chosen wire gauge meets both the voltage drop requirement AND the ampacity requirement for your current. The calculator checks both conditions and uses the more conservative (larger) gauge as the recommendation.

Should I use stranded or solid wire for solar systems? ▼

Use stranded wire for all solar system wiring. Stranded wire is more flexible, handles vibration better (important in RV/van/boat applications), makes better connections in lugs and terminal blocks, and is required by most equipment manufacturers for wiring to inverters, charge controllers, and battery terminals. Solid wire is only appropriate for permanent conduit runs in residential AC wiring. For all DC solar wiring, use stranded copper, preferably with fine-stranded marine-grade or solar-specific wire for critical runs.