EV Charger Installation Cost Calculator
Estimate a home charger install.
Special
EV Charger Circuit Size Calculator
Enter your Level 2 charger’s output current and the wire run to see the breaker size, the minimum copper or aluminum conductor, voltage drop over the distance and how many miles of range an hour of charging adds.
How it works
- Enter the charger’s output current — the amps it delivers continuously, set in its app or with a dial.
- Choose the supply voltage and whether the charger is hardwired or plugs into a receptacle.
- Choose the wire type and enter the one-way length from the panel to the charger.
- Read the breaker size and conductor, and check the voltage drop for long runs.
Formula
Circuit rating ≥ charger current × 125% Breaker = next standard size (15, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100 A…) Conductor ampacity ≥ breaker rating Voltage drop % = 2 × length × current × R ÷ 1,000 ÷ volts × 100
EV charging is treated as a continuous load, so the branch circuit is rated at least 125% of the charger’s output (NEC 625.41 and 210.19/210.20 in recent editions). Ampacities are from NEC Table 310.16 (75 °C column for copper THHN and aluminum, 60 °C for NM-B cable), with the small-conductor limits of 15/20/30 A for 14/12/10 AWG copper. R is conductor resistance in ohms per 1,000 ft from NEC Chapter 9, Table 8. Wire is upsized if voltage drop at the charger current exceeds 3%. Range per hour assumes 90% charging efficiency.
Example
A 40 A plug-in charger on a NEMA 14-50 receptacle, fed with NM-B cable 65 ft from the panel, for an EV that averages 3.2 miles per kWh.
Inputs
- Charger output current
- 40 A
- Supply voltage
- 240 V (single-phase)
- Connection
- Plug-in (14-50 / 6-50)
- Wire type
- Copper NM-B cable (60 °C)
- One-way wire length
- 65 ft
- Vehicle efficiency
- 3.2 mi/kWh
Result
Circuit for this charger50 A breaker · 6 AWGNM-B cable, 2-pole 240 V, receptacle
Charging power9.6 kW
Range added per hour≈ 28 mi
Voltage drop1.1%
Why a 48 A charger needs a 60 A breaker
A charger can run at full current for hours, so the circuit must be rated for 125% of that current: 48 A × 1.25 = 60 A. The same rule gives 40 A → 50 A, 32 A → 40 A and 24 A → 30 A. Most smart chargers let an installer lower the output to fit the breaker that is available.
Plug-in installations are capped at 50 A by the receptacle, so a plug-in charger normally runs at 40 A or less. Hardwiring allows 48 A and above and avoids receptacle wear.
Planning only — confirm with a licensed electrician
Your service size and existing loads decide whether the panel can take the new circuit; a load calculation or an energy management system may be needed. Terminal temperature ratings, conduit fill, ambient temperature, wet locations and local amendments can all change the conductor size. Based on the entered information, a load review or panel upgrade may be required — final sizing should be confirmed by a licensed electrician.
Frequently asked questions
What size breaker do I need for a 48 amp EV charger?
Typically a 60 A two-pole breaker, because the circuit must be rated at 125% of the 48 A continuous load. With copper THHN in conduit, 6 AWG is the usual minimum conductor.
What size wire for a 40 amp EV charger?
A 40 A charger needs a 50 A circuit. That is usually 8 AWG copper THHN in conduit (75 °C) or 6 AWG NM-B cable (60 °C). Long runs may need a larger size for voltage drop.
Can I plug a 48 A charger into a 14-50 outlet?
No. A NEMA 14-50 receptacle is limited to a 50 A circuit, which supports at most a 40 A continuous charger. A 48 A charger must be hardwired on a 60 A circuit.
Does my panel have room for an EV charger?
It depends on the service size and existing loads. An electrician performs a load calculation; if capacity is tight, a lower charger setting, an energy management system or a service upgrade may be options.
How many miles per hour does a Level 2 charger add?
Roughly kW × 0.9 × miles per kWh. A 48 A charger at 240 V (11.5 kW) adds about 35 miles of range per hour for an EV that averages 3.5 mi/kWh.