What size wire do I need for 30 amp 220v?

A 30 amp 220V circuit needs 10 gauge copper. That covers dryers, water heaters, mini splits, and RV receptacles, on a double-pole 30 amp breaker.

The cable choice follows the appliance: 10/2 for pure 240V loads like a water heater, 10/3 when the appliance also needs a neutral, like a four-prong dryer. Modern dryer receptacles are four-wire; the old three-prong setup is grandfathered only.

Distance changes the answer. Past about 80 feet at full load, voltage drop argues for 8 gauge, and a 70 foot run sits close enough to the line that the calculator is worth ten seconds.

Aluminum needs 8 AWG minimum for the same circuit.

Check your exact run with the 240V wire amperage calculator before buying cable.