EV Charger Circuit Calculator
Size a Level 2 EV charger circuit per NEC 625. Get the minimum breaker and copper or aluminum wire from the 125% continuous-load rule, plus charging power in kW and approximate miles added per hour. Free, no sign-up.
What to calculate next
Tools commonly used alongside this calculation
Wire Size & Ampacity Calculator
Find the minimum copper or aluminum wire size for a load using NEC Table 310.16, with 310.15 ambient and conductor-count derating and the 110.14(C) terminal limit. Free, no sign-up.
Voltage Drop Calculator
Calculate voltage drop % and the minimum copper or aluminum wire size to stay within the NEC 3% / 5% recommendation, single- or three-phase. Free, no sign-up.
Conduit Fill Calculator
Size conduit per NEC Chapter 9. Add THHN, XHHW, or other conductors and get the minimum trade size and fill % for EMT, IMC, RMC, PVC, ENT, FMC, and LFMC. Free, no sign-up.
Explanation
A Level 2 EV charger (the EVSE, electric vehicle supply equipment) runs at its full rated current for hours at a time, so NEC Article 625 treats it as a continuous load. That single fact drives the whole circuit: the breaker and the wire must be sized for 125% of the charger’s rated current, not 100%. This calculator takes the EVSE nameplate amps and returns the minimum breaker, the minimum conductor, and the charging power and speed.
The 125% continuous-load rule
NEC 625.41 and 625.42 require the branch circuit and the overcurrent device to carry at least 125% of the EVSE maximum load. Multiply the charger amps by 1.25, then round up to the next standard breaker size in NEC 240.6(A). The conductor is sized the same way — its 75 °C ampacity must meet that 125% value.
Breaker = next standard size ≥ circuit ampacity (NEC 240.6(A))
| Charger current | Circuit (×1.25) | Breaker | Copper wire (75 °C) |
|---|---|---|---|
| 32 A | 40 A | 40 A | 8 AWG |
| 40 A | 50 A | 50 A | 8 AWG |
| 48 A | 60 A | 60 A | 6 AWG |
To see exactly how the conductor is chosen — terminal temperature, ambient correction, and conductor count — open the wire size & ampacity calculator.
Hardwired vs. plug-in, and GFCI
A hardwired EVSE can run on a circuit sized for its full rating. A plug-in (cord-and-plug) unit on a NEMA 14-50 or similar receptacle is limited to 80% of the receptacle rating — a 50 A outlet supports a 40 A charger, which is why many plug-in units cap there. NEC 625.54 requires GFCI protection for cord-and-plug EVSE, so a plug-in install needs a GFCI breaker at the panel.
Charging power is simply voltage times current: a 48 A charger at 240 V delivers about 11.5 kW, which adds roughly 35–45 miles of range per hour depending on the vehicle’s efficiency. The grounding conductor for the circuit is sized separately — use the ground wire (EGC) size calculator.
Notes and limits
On a long run to a detached garage, the conductor that satisfies the 125% rule may still drop too much voltage — keep the branch circuit under about 3% and upsize a gauge if needed. The breaker sized here is the minimum continuous-load value; verify the EVSE instructions, which sometimes specify a particular breaker, and confirm the panel has the spare capacity with a service load calculation. Always check the final design against the current NEC and the authority having jurisdiction.