Wiring
EV charger circuit calculator
An EV charger is a continuous load, so the circuit is 125% of the charger's amps: a 48 A charger needs a 60 A breaker, a 40 A charger a 50 A breaker, and a 32 A charger a 40 A breaker. Wire size depends on cable type: in NM-B, a 48 A charger needs 4 AWG copper.
60 A · 4 AWGcopper, NM-B cable (Romex), indoors
- Charger output
- 48 A × 240 V = 11.5 kW
- Range added per hour
- 36 miles
- Time to add 40 miles
- 1.1 h
- Electricity cost per 100 miles
- $5.77
- Plug or hard-wire
- Must be hard-wired (over 40 A, no plug)
Check your panel has room: add this load to a NEC 220.83 load calculation, or ask about a load-management device before upgrading the service.
How the circuit is sized
circuit amps = charger amps × 1.25 (NEC 625.41, continuous load) breaker = next standard size wire = Table 310.16, column by cable type, then voltage drop ≤ 3% kW = charger amps × 240 V ÷ 1,000 miles/hour = kW × 0.9 charging efficiency × car mi/kWh
Level 2 charger sizes
Computed for a 20 ft run at 240 V with a 3.5 mi/kWh car.
| Charger | Power | Breaker | Copper NM-B | Copper THHN 75 °C | Range per hour |
|---|---|---|---|---|---|
| 16 A | 3.8 kW | 20 A | 12 AWG | 12 AWG | 12 mi |
| 24 A | 5.8 kW | 30 A | 10 AWG | 10 AWG | 18 mi |
| 32 A | 7.7 kW | 40 A | 8 AWG | 8 AWG | 24 mi |
| 40 A | 9.6 kW | 50 A | 6 AWG | 8 AWG | 30 mi |
| 48 A | 11.5 kW | 60 A | 4 AWG | 6 AWG | 36 mi |
| 64 A | 15.4 kW | 80 A | 3 AWG | 4 AWG | 48 mi |
| 80 A | 19.2 kW | 100 A | 1 AWG | 3 AWG | 60 mi |
Chargers above 40 A cannot use a plug: a NEMA 14-50 receptacle is limited to a 50 A circuit, which supports at most a 40 A charger, so 48 A and up are hard-wired. Plug-in chargers on a 14-50 should use an industrial-grade receptacle, and NEC 210.8(F) and 625.54 now require GFCI protection for EV receptacles.
What charging costs
At the U.S. average residential price of 18.19¢/kWh (EIA, January–July 2026), a 3.5 mi/kWh car costs about $5.77 per 100 miles charged at home. In California, at 33.25¢, it is $10.56; in Idaho, at 12.96¢, $4.11. Pick your state in the calculator, or see electricity prices by state.
Do you need the biggest charger?
Usually not. A 32 A charger adds about 24 miles per hour, which refills a 40-mile commute in under two hours. Larger chargers matter for long daily drives, trucks and households sharing one charger. A smaller circuit also leaves room in your panel; many homes with 100 A or 150 A service can add a 40 A circuit without a service upgrade after a NEC 220.83 load calculation.
Safety. EV charger circuits need a permit in almost every US jurisdiction. Follow the charger manufacturer's installation manual: it states the required breaker size and wire, and it overrides any general calculation.
Common questions
What size wire for a 48 amp EV charger?
4 AWG copper in NM-B cable, or 6 AWG copper THHN in conduit with 75 °C terminations, on a 60 A breaker. Long runs may need one size up for voltage drop.
What size breaker for a 40 amp EV charger?
50 A. 40 A × 1.25 = 50 A. Use 6 AWG copper in NM-B or 8 AWG copper THHN at 75 °C.
Can I use a NEMA 14-50 outlet for my EV?
Yes, for a charger set to 40 A or less, on a 50 A circuit with GFCI protection. Use a heavy-duty receptacle rated for continuous use; cheap ones overheat.
Guides that use this calculator
- How Much Does It Cost to Charge an EV at Home? (By State)
- What Size Wire for 50 Amps? Why NM-B Uses the 60 °C Column