How Many Watts Is 40 Amps?
40 A is 9,600 W at 240 V DC. At other common voltages — 120 V: 4,800 W. Use the calculator below for any voltage or circuit type.
Real example: a 40 A range or Level 2 EV charger
40 A circuits (8 AWG copper) power electric ranges and Level 2 EV chargers. At 240 V a 40 A breaker carries 9,600 W; because an EV charger is a continuous load it is limited to 32 A / 7,680 W.
40 Amps to Watts — Voltage Reference Chart
| Voltage | Power (PF 1) | Typical use |
|---|---|---|
| 12 V | 480 W | 12V DC / automotive |
| 120 V | 4,800 W | US household standard |
| 208 V | 8,320 W | 208V commercial (L-L) |
| 240 V | 9,600 W | US/EU 240V circuit |
| 480 V | 19,200 W | Industrial 3-phase (L-L) |
Wire & breaker: A 40 A circuit is normally run in 8 AWG copper. Remember the NEC 80% rule for continuous loads (3 hours+): usable power is 9,600 × 0.8 = 7,680 W at 240 V. Background: watts vs amps. Always confirm with a licensed electrician.
In practice: breaker rating versus deliverable power
Forty amps over 8 AWG copper gives 9,600 W at 240 V, but an EV charger may only use 32 A of it because continuous loads are capped at 80%. That is where the familiar 7,680 W Level 2 figure comes from — the same breaker, a different usable ceiling. Treating the breaker rating as available continuous power is the most frequent planning error on charger installs.
Frequently Asked Questions
How many watts is 40 amps at 120V?
At 120V, 40 A delivers 40 × 120 = 4,800 watts (resistive, PF 1). For a continuous load the NEC limits this to 80%: 3,840 W. For AC with a power factor below 1, multiply by PF.
How many watts is 40 amps at 240V?
At 240V, 40 A delivers 40 × 240 = 9,600 watts; the 80% continuous limit is 7,680 W.
How many watts is a 40 amp EV charger circuit?
A 40 A, 240 V circuit is rated 9,600 W, but an EV charger (a continuous load) may only use 80%: 7,680 W, i.e. 32 A. That is exactly why a "40 A" wallbox charges at 7.7 kW. Size the reverse — power to current — with kW to amps.