EV Charger Circuit Amps Calculator
Find the breaker size and circuit amps your home EV charger needs under the 125% continuous-load rule, plus the real charging power it delivers.
How it works
Required circuit = charger amps ÷ 0.8 (125% continuous rule) · Breaker = next standard size ≥ required · Power = amps × volts ÷ 1000
EV charging is a "continuous load" — current flowing for three hours or more — and electrical code requires the circuit and breaker to be rated at 125% of a continuous load. That is the same as dividing the charger's draw by 0.8: a 40 A charger needs a 50 A circuit, so it may only ever pull 80% of the breaker rating. The delivered power is simply amps times volts, which is why a 240 V Level 2 circuit charges many times faster than a 120 V Level 1 outlet at the same amperage.
Worked example
A 40 A EV charger is continuous, so the circuit must be rated 40 ÷ 0.8 = 50 A, meaning a 50 A breaker with appropriately sized wire. At 240 V it delivers 40 × 240 = 9,600 W, or 9.6 kW — roughly 30–35 miles of range added per hour on a typical EV.
Frequently asked questions
Why does a 40 A charger need a 50 A breaker?
Because EV charging runs for hours, code classifies it as a continuous load and requires the circuit to be rated at 125% of that load. 125% of 40 A is 50 A, so a 50 A breaker (with matching wire) is required even though the charger never draws more than 40 A.
What wire gauge do I need?
It follows the breaker, not just the charger current, and depends on wire type and run length. As a rough guide a 50 A circuit typically uses 6 AWG copper; always confirm with an electrician against local code, since voltage drop on long runs can require going a size larger.
How much faster is 240 V than 120 V?
At the same amperage, exactly twice the power, and in practice far more usable: a 120 V Level 1 outlet adds only 3–5 miles of range per hour, while a 240 V Level 2 circuit at 40 A adds 25–35. Level 2 is what makes overnight home charging fully replenish a daily commute.
Related calculators
Educational estimate only — EV circuits must be installed and verified by a licensed electrician to local code.