Solar Wire Size Calculator

Q: What size wire do I need for my solar panels?

It depends on the current (amps), the cable length, and your system voltage. Longer runs and lower voltages need thicker wire to keep voltage drop under about 3 percent. Enter your numbers in the calculator to get the exact gauge in AWG and mm², checked against both voltage drop and ampacity.

Q: What is a good voltage drop for solar wiring?

Aim for 3 percent or less on the main DC runs, and 2 percent or less on critical circuits such as panel-to-charge-controller. A lower voltage drop means less wasted energy but needs thicker, more expensive wire.

Q: Why does a 12V system need such thick wire?

For the same power, lower voltage means higher current, and voltage drop grows with current. A 12V system carries four times the current of a 48V system for the same watts, so it needs much thicker cable over the same distance. Raising the system voltage is often cheaper than buying huge cable.

Q: Should I size wire for voltage drop or ampacity?

Both. Ampacity is the current a wire can carry safely without overheating, and it sets the minimum for safety. Voltage drop often demands an even thicker wire on long runs. This calculator checks both and recommends whichever is larger.

Find the right wire gauge for your solar wiring. Enter your voltage, current, cable length and target voltage drop, and get the size in AWG and mm² with an ampacity safety check.

System voltage (V — 12, 24 or 48 typical)

Current (amps)

Cable length, one way

Unit

Max voltage drop (% — 3 is typical)

Conductor material

Recommended wire size

Wire gauge

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Cross-section

—

Voltage drop

—

Drop in volts

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Nearby wire sizes for this run

AWG	mm²	Voltage drop	Ampacity

Ampacity shown is adjusted for the chosen material. A check mark means the wire can safely carry your current; a cross means it cannot.

How to use this solar wire size calculator

Enter four things and the calculator returns the right wire gauge instantly:

System voltage — 12, 24 or 48 V for most DIY and off-grid solar.
Current in amps — the maximum current the wire will carry (for a panel, use its short-circuit current Isc; for a load, its running current).
Cable length, one way — the distance from source to load. The calculator doubles it automatically for the return path.
Max voltage drop — 3% is the common target, 2% for critical runs.

The result is given in AWG (American Wire Gauge) and mm², and is checked against both voltage drop and ampacity. The thicker of the two wins.

How wire size is calculated

Two separate limits decide the wire size, and you must satisfy both.

1. Voltage drop

Thin wire and long runs waste energy as heat. The cross-section needed to stay within your voltage-drop target is:

area (mm²) = (2 × length × current × ρ) ÷ (voltage × drop% ÷ 100)

where ρ is the resistivity of the metal (copper ≈ 0.0175, aluminium ≈ 0.0282 Ω·mm²/m) and the length is doubled to account for the return conductor.

2. Ampacity

Ampacity is the current a wire can carry continuously without overheating. Even a short run must meet it for safety. This tool uses a copper ampacity table for 90 °C-rated insulation (aluminium is derated by about 22%). On long runs, voltage drop usually demands a thicker wire than ampacity alone.

Why 12V systems need thick wire

Power equals voltage times current. For the same power, a 12 V system carries four times the current of a 48 V system, and voltage drop rises with current. That is why the same 200 W load needs far heavier cable at 12 V than at 48 V over the same distance. If your wire size comes out huge, raising the system voltage is often cheaper than buying massive cable.

Frequently asked questions

What size wire do I need for my solar panels?

It depends on the current, the cable length and your system voltage. Longer runs and lower voltages need thicker wire to keep voltage drop under about 3%. Enter your numbers above to get the exact gauge in AWG and mm².

What is a good voltage drop for solar wiring?

Aim for 3% or less on the main DC runs, and 2% or less on critical circuits such as panel-to-charge-controller. Lower drop wastes less energy but needs thicker, pricier wire.

Why does a 12V system need such thick wire?

Lower voltage means higher current for the same power, and voltage drop grows with current. A 12V system carries four times the current of a 48V system for the same watts, so it needs much thicker cable over the same distance.

Should I size wire for voltage drop or ampacity?

Both. Ampacity sets the minimum for safety; voltage drop often demands an even thicker wire on long runs. This calculator checks both and recommends whichever is larger.

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Setting up a system? Also find the optimal solar panel angle for your location to get the most energy from your panels.