How Many Watts Is 40 Amps?
A 40 A circuit at 120 V carries 4,800 W (3,840 W continuous), and at 240 V carries 9,600 W. Multiply amps × volts (× power factor for AC). Use the calculator below for any voltage.
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.
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.