How Many Amps Is 3 kW?
3 kW is 12.50 A at 240 V DC. At other common voltages — 120 V: 25.00 A. Use the calculator below for any voltage or circuit type.
Real example: a 3 kW tankless water heater
3 kW single-phase is a common tankless / immersion water-heater and small-appliance rating. As a resistive load at 240 V it draws 12.5 A; at 120 V it would be 25 A. (3 kW is also roughly 4 HP of motor output.)
3 kW to Amps — Reference Chart
| Circuit | Voltage | PF | Amps |
|---|---|---|---|
| DC | 120 V | — | 25.0000 A |
| DC | 240 V | — | 12.5000 A |
| DC | 480 V | — | 6.2500 A |
| AC 1Ø | 120 V | 1.0 | 25.0000 A |
| AC 1Ø | 240 V | 1.0 | 12.5000 A |
| AC 1Ø | 240 V | 0.8 | 15.6250 A |
| AC 3Ø (L-L) | 208 V | 0.8 | 10.4090 A |
| AC 3Ø (L-L) | 400 V | 0.8 | 5.4127 A |
| AC 3Ø (L-L) | 480 V | 0.8 | 4.5105 A |
Wire & breaker: At 240 V, 3 kW resistive draws 12.5 A; at NEC 125% that is 15.6 A, so a 20 A breaker on 12 AWG copper is correct. Always confirm with an electrician. Background: watts vs amps.
In practice: the 3 kW limit on a 13 A plug
Three kilowatts is the practical ceiling for anything on a standard UK 13 A plug: at 230 V it works out to 13.04 A, sitting right on the fuse rating. This is exactly why domestic kettles cluster at 2.8–3 kW and never climb higher. Anything above it — an electric shower, a cooker — has to be hard-wired onto its own circuit rather than plugged in.
Frequently Asked Questions
How many amps is 3 kW at 240V single-phase?
3 kW at 240V DC or PF 1 = (3 × 1,000) ÷ 240 = 12.5000 amps. For AC single-phase with PF 0.8: 3,000 ÷ (240 × 0.8) = 15.6250 amps.
How many amps is 3 kW on a 400V three-phase supply?
3 kW on 400V three-phase at PF 0.8 = (3 × 1,000) ÷ (√3 × 400 × 0.8) = 5.4127 amps per phase. At unity PF: 4.3301 amps.
What breaker size does a 3 kW water heater need?
A 3 kW resistive heater at 240 V draws 12.5 A. Continuous loads are sized at 125%: 12.5 × 1.25 = 15.6 A, so a 20 A breaker with 12 AWG copper is the right choice. Reverse the calc with amps to kW.