kW vs amps
Amps measure current; kilowatts measure power, which is what actually determines charging speed. At 240 V, power in kW is amps × 240 ÷ 1000 — so a 48 A charger delivers 11.5 kW.
Charger marketing mixes both units. Convert with kW = A × V ÷ 1000: 32 A → 7.7 kW, 40 A → 9.6 kW, 48 A → 11.5 kW, 80 A → 19.2 kW (all at 240 V).
Your vehicle’s onboard charger sets a kW ceiling. If the car accepts 10.5 kW, a 19.2 kW wall charger charges it no faster than an 11.5 kW one.
| Amps → kW | kW = amps × volts ÷ 1,000 |
|---|---|
| kW → amps | amps = kW × 1,000 ÷ volts |
| At 240 V | 16 A = 3.8 kW · 24 A = 5.8 kW · 32 A = 7.7 kW · 40 A = 9.6 kW · 48 A = 11.5 kW · 80 A = 19.2 kW |
| At 208 V | 32 A = 6.7 kW · 40 A = 8.3 kW · 48 A = 10.0 kW · 80 A = 16.6 kW |
| Reverse, at 240 V | 6.6 kW = 27.5 A · 10.5 kW = 43.8 A · 11 kW = 45.8 A · 11.5 kW = 47.9 A · 19.2 kW = 80 A |
| At 120 V (Level 1) | 12 A = 1.44 kW · 16 A = 1.92 kW |
The formula, and why 240 is the right number to use
Power in watts is volts × amps; divide by 1,000 for kilowatts. For a home Level 2 circuit the voltage is 240 V nominal, taken across the two hot legs of a split-phase residential service. Actual utility voltage typically measures 235–245 V and sags a few volts under a sustained 40–48 A load, so a “11.5 kW” charger might really deliver 11.2 kW on a warm evening. That is normal and not worth chasing.
Manufacturers round in both directions, which is where the confusion starts. 48 A × 240 V is exactly 11,520 W, sold variously as 11.5 kW, 11.52 kW or “11 kW”. 40 A is exactly 9.6 kW but appears as “9.6 kW” or “up to 10 kW”. When two spec sheets disagree, convert from the amperage — that is the number the hardware and the breaker are actually built around.
The one voltage that changes the answer materially is 208 V, standard in apartment buildings and commercial garages on a three-phase wye service. Every conversion drops by 13%: a 48 A charger delivers 9.98 kW instead of 11.52 kW, and 80 A gives 16.6 kW instead of 19.2 kW. Never compute with 250 V, which appears on receptacle nameplates as a maximum voltage rating, not as a supply voltage.
Going backwards: turning a kW spec into amps
Vehicles publish their AC limit in kilowatts; chargers and breakers are sold in amps. To bridge them, divide the car’s kW by 240. A 10.5 kW Ford Mustang Mach-E draws 43.75 A. A 10.9 kW Hyundai Ioniq 5 draws 45.4 A. An 11 kW BMW i4 draws 45.8 A. An 11.5 kW Tesla Model Y draws 47.9 A. A 6.6 kW Nissan Leaf draws 27.5 A.
Then round up to the next standard charger size, because you cannot buy a 43.75 A charger. Chargers come in 16, 24, 32, 40, 48 and 80 A. The 10.5 kW Mach-E therefore wants a 48 A unit; a 40 A unit would cap it at 9.6 kW and leave 0.9 kW unused. The 6.6 kW Leaf wants a 32 A unit and gains literally nothing from anything larger.
Finally apply the 125% continuous-load rule to get the breaker: 32 A charger → 40 A breaker, 40 A → 50 A, 48 A → 60 A, 80 A → 100 A. Run the chain in that order — car kW, then amps, then charger size, then breaker — and you will not overbuy. Running it backwards, starting from “what breaker can my panel take”, is how people end up with a 19.2 kW charger feeding an 11.5 kW car.
kW, kWh, and the third unit people mix up
A kilowatt is a rate; a kilowatt-hour is a quantity. Your charger has a kW rating, your battery has a kWh capacity, and your electricity bill is denominated in kWh. Time in hours is simply capacity divided by rate: a 75 kWh pack on an 11.5 kW charger is 75 ÷ 11.5 ≈ 6.5 hours from empty, and a 205 kWh Silverado EV on the same charger is nearly eighteen.
The meter reads more than the pack gains. AC Level 2 charging runs at roughly 85–92% wall-to-battery efficiency once you account for the onboard charger’s conversion losses, the coolant pumps, and the 12 V systems the car keeps awake. Putting 60 kWh into the battery costs about 65–70 kWh at the meter. Cold weather makes it worse, sometimes much worse, because the car spends real energy warming the pack before and during charging.
For range, add one more multiplier: miles per kWh. Charging power × efficiency gives miles per hour of charging. Eleven and a half kilowatts on a car doing 3.5 mi/kWh is about 40 miles an hour; the same 11.5 kW on a 2 mi/kWh electric truck is 23. This is why a charger advertising “up to 44 miles per hour” is quoting the best case for an efficient sedan and telling you nothing about your car.
Frequently asked questions
How many amps is 11.5 kW?
47.9 amps at 240 V (11,500 ÷ 240). In practice that is a 48 A charger on a 60 A breaker, which is the mainstream home configuration because 11.5 kW is the onboard limit of most current EVs. At 208 V the same 11.5 kW would need 55 A, which is why 208 V installations cannot reach it with standard 48 A hardware.
What is 10.5 kW in amps?
43.75 amps at 240 V. Because chargers are sold in fixed sizes, a 10.5 kW car — the Ford Mustang Mach-E, for example — needs a 48 A charger to be fully saturated. A 40 A charger delivers 9.6 kW and leaves about 0.9 kW on the table, which is roughly 9% slower.
How many kW is a 48 amp EV charger?
11.52 kW at 240 V, usually written as 11.5 kW. On a 208 V supply the same charger delivers 9.98 kW. Note the ceiling is the lower of the charger and the car: a 48 A charger feeding a 6.6 kW Nissan Leaf still only moves 6.6 kW.
Is 19.2 kW the same as 80 amps?
Yes, at 240 V: 80 × 240 = 19,200 W. An 80 A charger requires a 100 A dedicated circuit under the 125% continuous-load rule, must be hardwired, and only three current EVs — the extended-range F-150 Lightning, the Silverado EV and the Lucid Air — can actually accept 19.2 kW on AC.
Why does my charger deliver fewer kW than its rating?
Four common reasons, in order of likelihood: your car’s onboard charger is the lower limit; the supply is 208 V rather than 240 V; voltage sags under load on a long or undersized run; or the charger is set below its maximum by a DIP switch or app setting. The charger reports what it is delivering — compare that against amps × measured volts before assuming a fault.