Solar Panel Wire Size Calculator
Free solar panel wire size calculator. Enter voltage, current, and run length to get the smallest AWG that stays under your max voltage drop.
Solar Wire Size Calculator
How to use this calculator
Enter your circuit details:
- System voltage — 12 V / 24 V / 48 V for off-grid, or your PV string voltage
- Current — maximum amps the circuit carries
- One-way length — distance from source to load in feet
- Max voltage drop % — typically 3% for NEC compliance, 2% if you want excellent
The calculator finds the smallest AWG that keeps drop within your target. Smaller wire = cheaper. Bigger wire if no smaller size works for your run.
Why wire size matters more than most people realize
A solar wire that’s too small does three bad things:
- Wastes electricity as heat
- Reduces voltage at the load — inverters can disconnect, charge controllers can underperform
- Heats up under load — long-term, this degrades insulation and can become a fire risk
Going one size larger than you think you need is one of the cheapest performance upgrades on a DIY solar install — copper costs are linear-ish, but performance gains are much larger.
The math behind the answer
The calculator tries every standard AWG (14, 12, 10, 8, 6, 4, 2, 0) and computes the voltage drop for your inputs. It then picks the smallest wire (highest AWG number) that keeps drop within your specified percentage.
Voltage drop formula:
V_drop = 2 × Length(m) × Resistance(Ω/m) × Current(A)Each AWG step roughly halves resistance, so going from 10 AWG to 8 AWG cuts your voltage drop by about 37%.
Typical 12 V solar wire sizes
| Run length | 5 A | 10 A | 20 A | 30 A |
|---|---|---|---|---|
| 5 ft | 14 AWG | 14 AWG | 12 AWG | 10 AWG |
| 10 ft | 14 AWG | 12 AWG | 10 AWG | 8 AWG |
| 25 ft | 12 AWG | 10 AWG | 8 AWG | 6 AWG |
| 50 ft | 10 AWG | 8 AWG | 6 AWG | 4 AWG |
| 100 ft | 8 AWG | 6 AWG | 4 AWG | 2 AWG |
These assume 3% max drop on 12 V DC. Going to 24 V or 48 V cuts the wire size requirement dramatically — at 48 V, you can use wire two or three sizes smaller for the same load.
Voltage drop vs ampacity — pick the larger size
Two separate constraints govern wire choice:
- Ampacity: the wire must safely carry the current without overheating. Set by NEC Table 310.16, with derating for temperature and conduit fill.
- Voltage drop: the wire must keep the load above its minimum voltage. Set by your design choice (3% is typical).
For long runs, voltage drop usually wins (you need bigger wire than ampacity demands). For short, high-current runs, ampacity wins.
Always use the larger of the two requirements.
This calculator handles voltage drop. For ampacity, consult the NEC tables or have a licensed electrician verify your design.