A charger’s kilowatts are calculated, not assigned. For single-phase AC, kW = volts × amps ÷ 1,000: a 40 A charger on 240 V is 240 × 40 ÷ 1,000 = 9.6 kW. Three-phase uses a different form of the same maths — which is how a 16 A charger can honestly be rated 11 kW.
Key Takeaways
- Single-phase: kW = volts × amps ÷ 1,000. The rating on the box is this calculation.
- Three-phase adds a 1.73 factor: 16 A ≈ 11 kW and 32 A ≈ 22 kW at 400 V.
- kW is the rate; multiply by hours to get kWh, the energy your battery receives.
- Delivered power is the lowest of the charger, the circuit and the car’s own limit.
The Single-Phase Calculation
Volts are electrical pressure, amps are flow; their product is power in watts, and watts ÷ 1,000 is kilowatts. Run the formula across the common home settings and you reproduce the ratings on product pages.
| Charger current | Supply voltage | Calculation | Power |
|---|---|---|---|
| 16 A | 240 V | 16 × 240 ÷ 1,000 | 3.8 kW |
| 32 A | 240 V | 32 × 240 ÷ 1,000 | 7.7 kW |
| 40 A | 240 V | 40 × 240 ÷ 1,000 | 9.6 kW |
| 48 A | 240 V | 48 × 240 ÷ 1,000 | 11.5 kW |
Voltage is half the answer: at 208 V — common at North American commercial sites — 32 A gives 32 × 208 ÷ 1,000 ≈ 6.7 kW, one reason public Level 2 can feel slower than the same charger at home. For ratings by level, see how many kW a Level 2 charger delivers.
The Three-Phase Calculation
On three-phase, three conductors share the work, and the formula becomes kW ≈ 1.73 × line volts × amps ÷ 1,000. European three-phase runs at 400 V line voltage:
- 16 A three-phase: 1.73 × 400 × 16 ÷ 1,000 ≈ 11 kW.
- 32 A three-phase: 1.73 × 400 × 32 ÷ 1,000 ≈ 22 kW.
- 32 A single-phase at 230 V: 32 × 230 ÷ 1,000 ≈ 7.4 kW — same current, one phase, a third of the power.
That is the whole secret behind Europe’s 7, 11 and 22 kW home chargers: the current barely changes; the phases do. Our comparison of single-phase and three-phase charging covers what each means for charging time.
kW Is a Rate; kWh Is the Amount
The calculation gives a rate of flow. Energy — what your battery actually receives — is rate × time: kWh = kW × hours. At 7.7 kW for five hours, ideal arithmetic delivers about 38.5 kWh; real sessions vary as the car manages the charge. Your battery is sized in kWh, the charger in kW, and time bridges them — which is why how many kWh a charge takes is a separate question.
Why the Label Is a Maximum, Not a Promise
The formula gives the charger’s ceiling. What your car actually receives is the lowest of three numbers:
- The charger’s calculated rating — volts × amps, as above.
- The circuit behind it. Charging is a continuous load under the National Electrical Code, so breakers are sized at 125 percent of charger current: 32 A → 40 A breaker, 48 A → 60 A. See how many amps an EV charger needs.
- The car’s onboard charger. For AC charging the car converts and limits the power: a car accepting 7.2 kW takes about 7.2 kW from any AC charger.
The Calculation, Applied to EVDANCE Chargers
The EV-ACS3210T 32A NACS portable charger is rated at about 7.7 kW — that is 32 A × 240 V. The EV-ACT5006T 48A Level 2 wall charger reaches 48 × 240 ÷ 1,000 ≈ 11.5 kW. The ACS1605PE 11 kW three-phase portable charger gets its rating the three-phase way, at 16 A per phase. Each product number is the formula with that unit’s current and supply filled in.
Frequently Asked Questions
Why does a 32 A charger say 7.4 kW in Europe and 7.7 kW in North America?
Voltage. Single-phase supplies are nominally 230 V in Europe and 240 V in North America: the same 32 A gives ≈ 7.4 kW in one market and ≈ 7.7 kW in the other. The charger did not change; the supply did.
Is a DC fast charger’s kW calculated the same way?
The rating still describes power delivered to the car — the U.S. Department of Transportation puts DC fast charging at 50–350 kW. The difference: the AC-to-DC conversion happens inside the station, so you read its output rating instead of calculating from your supply.
If I double the amps, do I double the kW?
At the same voltage, yes — the relationship is linear. Whether you get it in practice depends on the circuit and the car’s onboard limit.
Related Reading
- How Many kW Is a Level 2 Charger?
- How Many kWh Does It Take to Charge an EV?
- How Many Amps Does an EV Charger Need?
- Single-Phase vs Three-Phase EV Charging: 7kW, 11kW and 22kW Explained
