Free EV charging calculators

Level 2 Charger Amps (Amps, kW and Breaker Size)

Enter a charger's amps, its kW or your breaker size to see the power, the breaker it needs and the range it adds each hour.

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This free Level 2 charger amps calculator converts between a charger’s amps, its power in kW and the breaker size its circuit needs, and it estimates how much range one hour of charging adds. It runs in your browser with no sign-up, and nothing you enter is uploaded. Level 2 chargers usually run on a 240 V circuit in North America or 230 V in Europe, so the same amp rating gives a different kW figure at each voltage. Enter the number you know, whether that is the charger’s amps, its kW or your breaker size, and the tool works out the rest. Example buttons let you test common setups such as a 32 A, 40 A or 48 A charger in one click.
Level 2 charger amps example

How to use the Level 2 charger amps calculator

  1. Open the “I know” drop-down and choose what you have: The charger’s amps, The charger’s kW or My breaker size.
  2. Type the matching value into the field that appears: Charger rated current (A), Charger power (kW) or Breaker size (A). Take the number from your charger’s label or data sheet.
  3. Check the Voltage (V) field. Keep 240 V for a North American supply or 230 V for Europe, or enter the voltage measured at your circuit if you know it.
  4. Optional: open More options. Enter the Car’s onboard charger limit (kW) if you know it, keep the Charging loss (%) at its 9.2 % default or enter your own estimate, and type your Car efficiency with its unit, such as 3.5 mi/kWh, to get miles per hour.
  5. Read the result rows: charger current, charger power, minimum breaker, highest charger current that breaker allows, power the car accepts, energy added per hour and range added per hour. Rows that do not apply to your chosen mode are hidden.
  6. Read any warning shown below the results, then compare your numbers with the common ratings table.

The example buttons above the form load a 32 A, 40 A and 48 A charger, an 11.5 kW charger and a 50 A breaker. Copy result copies the result lines with a link, and Copy link stores every input in the page address so the same calculation reopens later. Print / save as PDF prints the inputs, results, steps and date. Reset restores the starting example.

How many kW is a level 2 charger?

A Level 2 charger’s power in kW equals its voltage multiplied by its amps, divided by 1,000. On a 240 V circuit, a 16 A charger is 3.84 kW, a 32 A charger is 7.68 kW and a 48 A charger is 11.52 kW.

The formula also works in reverse: kW × 1,000 ÷ volts gives amps. For example, 11.5 kW at 240 V is about 47.92 A. The same 40 A charger produces 9.6 kW at 240 V but 9.2 kW at 230 V, so use the voltage that applies to your circuit.

How many amps is a level 2 charger?

A Level 2 charger’s amps are set by its rating, which is printed on its label or data sheet. The SAE J1772 standard’s AC Level 2 range tops out at 80 A, which is 19.2 kW at 240 V. The table under the result lists 16, 24, 30, 32, 40, 48, 50, 60 and 80 A; check your own charger’s label for its rating.

What size breaker do I need for a 40 amp EV charger?

You need a 50 amp double-pole breaker. An EV charger counts as a continuous load, so its circuit and breaker must be rated at at least 125 % of the charger’s current. For a 40 A charger, 40 × 1.25 = 50 A, which is already a standard breaker size.

A 50 A breaker allows the charger to draw up to 80 % of its rating, which is 40 A. That is exactly the 40 A charger’s rating, so the pair fits. The same 40 A charger delivers 9.6 kW at 240 V. A 32 amp charger needs a 40 A breaker, since 32 × 1.25 = 40 A exactly.

What size breaker do I need for a 48 amp charger?

You need a 60 amp breaker. A 48 A charger needs 48 × 1.25 = 60 A, which is a standard size, and at 240 V the charger then delivers 11.52 kW.

Check the breaker size before you buy a charger, because a larger breaker does not raise the charger’s own limit. The breaker only sets the maximum the circuit can carry.

Can a 50 amp breaker run a 48 amp charger?

No. A 50 amp breaker allows at most 80 % of its rating, which is 40 A, so a 48 A charger would overload it. You can set the calculator to My breaker size of 50 A to see the highest charger current it allows.

For a 48 A charger, use a 60 A breaker. For a 50 A breaker, choose a charger rated at 40 A or lower.

Worked examples

InputResult
40 A at 240 V40 A, 9.6 kW, breaker 50 A
32 A at 240 V32 A, 7.68 kW, breaker 40 A
48 A at 240 V48 A, 11.52 kW, breaker 60 A
11.5 kW at 240 V47.92 A, 11.5 kW, breaker 60 A
60 A breaker at 240 V48 A, 11.52 kW, breaker 60 A

Calculated by the tool above with these values.

Frequently asked questions

How many miles per hour does a level 2 charger add?

Range added per hour equals the kW the car accepts, multiplied by (1 minus the charging loss), multiplied by the car’s efficiency in miles per kWh. With the calculator’s default values of 9.2 % loss and 3.5 mi/kWh, a 40 amp charger adds about 30.5 miles per hour and a 32 amp charger about 24.4 miles.

Does a bigger level 2 charger always charge my car faster?

No. The car’s onboard charger limits the AC power it accepts, so a 48 A (11.52 kW) charger delivers only 11.5 kW to a car with an 11.5 kW limit. Enter the car’s limit under More options, and check your car’s manual, because many cars accept less than the highest chargers offer.

What is the highest current a Level 2 charger can use?

The top of the SAE J1772 AC Level 2 range is 80 A, or 19.2 kW at 240 V. The calculator shows a warning for any value above 80 A, so check the input if you see it.

Does this calculator size the wire or check my home’s electrical service?

No. The calculator covers amps, kW, breaker size and range per hour only. Use the EV charger wire size calculator for wire and the EV charger load calculator for load, and have a licensed electrician verify any installation.

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