Electrical sizing

Wire Gauge Calculator

Enter the current, the one-way length of the run, the voltage and the voltage drop you can accept. The calculator recommends the smallest AWG wire that meets both the ampacity and voltage drop limits.

—Recommended size
—Voltage drop
—Voltage at load
AWGmm²AmpacityDrop (V)Drop (%)Status

Calculated on your device. Nothing is uploaded to a server.

How to use the wire gauge calculator

  1. Describe the loadEnter the current in amps and the system voltage.
  2. Enter the runType the one-way distance from the source to the load and choose the conductor material.
  3. Read the sizeThe highlighted row is the smallest gauge that passes both checks.

How wire size is chosen

A wire must pass two checks. First, its ampacity has to cover the current so the insulation doesn't overheat. Second, its resistance over the length of the run must keep the voltage drop within your limit, usually 3% for a branch circuit. The calculator works out the voltage drop for every gauge from the conductor resistance per 1,000 feet. It uses the round-trip length for DC and single-phase circuits, and √3 times the one-way length for three-phase. It then picks the smallest gauge that passes both checks. Ampacity values are the common 75 °C column for copper and aluminum. For 14, 12 and 10 AWG, the calculator uses the usual 15, 20 and 30 A copper breaker limits.

Why distance matters

Voltage drop grows with both current and length. Long runs to sheds, pumps or low-voltage lighting often need a thicker wire than ampacity alone would suggest.

Always check local code

Insulation type, bundling, ambient temperature and local electrical codes can all change the right size. Treat this as a planning estimate and have a licensed electrician confirm it.

Wire Gauge Calculator FAQ

What voltage drop should I aim for?

A common guideline is up to 3% on a branch circuit and 5% in total from the service to the farthest outlet. Low-voltage DC systems such as 12 V solar often aim for 2 to 3%.

Should I enter the one-way or round-trip distance?

Enter the one-way distance from the source to the load. The calculator doubles it for DC and single-phase circuits and applies √3 for three-phase.

Why is 14 AWG limited to 15 A?

Most electrical codes limit overcurrent protection for small copper conductors to 15 A for 14 AWG, 20 A for 12 AWG and 30 A for 10 AWG, so the calculator uses those limits.

Can I use aluminum wire?

Yes. Choose aluminum. It has about 1.64 times the resistance of copper and lower ampacity, so it usually needs a size or two larger.

What if no size fits?

If even 4/0 fails, the run needs larger kcmil conductors, parallel runs, a higher voltage or a shorter distance.

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