Amps to Watts Calculator
Find real power in watts (and kW / kVA) from current, voltage and power factor for DC, single-phase and three-phase circuits.
Amps to watts formulas
Real power P (watts) is what does useful work and what your utility bills in kWh. Apparent power S = P / PF (volt-amperes) is what the wiring and transformer must carry. The calculator shows both for AC circuits so you can size generators and UPS units, which are usually rated in kVA.
Worked examples
DC: a 12 V device drawing 10 A uses 10 × 12 = 120 W.
Single-phase: a 120 V tool drawing 12 A with PF 0.85 uses 12 × 120 × 0.85 = 1,224 W real power, or 1.44 kVA apparent power.
Three-phase: a 480 V feeder carrying 13.36 A per line with PF 0.9 delivers 1.732 × 13.36 × 480 × 0.9 ≈ 10.0 kW.
Amps to watts reference table
| Current | 12 V DC | 120 V 1φ | 240 V 1φ | 208 V 3φ | 480 V 3φ |
|---|---|---|---|---|---|
| 1 A | 12 W | 120 W | 240 W | 360 W | 831 W |
| 5 A | 60 W | 600 W | 1,200 W | 1,801 W | 4,157 W |
| 10 A | 120 W | 1,200 W | 2,400 W | 3,603 W | 8,314 W |
| 15 A | 180 W | 1,800 W | 3,600 W | 5,404 W | 12,471 W |
| 20 A | 240 W | 2,400 W | 4,800 W | 7,205 W | 16,628 W |
| 30 A | 360 W | 3,600 W | 7,200 W | 10,808 W | 24,942 W |
| 50 A | 600 W | 6,000 W | 12,000 W | 18,013 W | 41,569 W |
| 100 A | 1,200 W | 12,000 W | 24,000 W | 36,027 W | 83,138 W |
PF = 1. Multiply by PF for real power of inductive loads.
How much power can a circuit supply?
A 15 A, 120 V household circuit can supply 1,800 W momentarily, but continuous loads should stay at or below 80%: 12 A, or 1,440 W. A 20 A, 120 V circuit gives 1,920 W continuous; a 30 A, 240 V circuit gives 5,760 W continuous. These limits are why most portable heaters are capped at 1,500 W.
Tips
- Measure current with a clamp meter on one conductor only; clamping both cancels the reading.
- For three-phase loads, average the three line currents if they are unbalanced.
- If a nameplate lists only VA or kVA, that already equals V × I; multiply by PF to get watts.
Frequently asked questions
How many watts is 10 amps?
At 120 V, 10 A is 1,200 W; at 240 V it is 2,400 W; at 12 V DC it is 120 W (assuming PF 1).
How many watts can a 15 amp breaker handle?
On 120 V, 15 A × 120 V = 1,800 W peak. For continuous loads the 80% rule limits it to 1,440 W.
What is the difference between watts and VA?
Watts are real power; VA is apparent power (V × I). Watts = VA × power factor. They are equal only for resistive loads.
How do I convert amps to kW for three-phase?
kW = √3 × I × V_LL × PF / 1000. For 50 A at 400 V and PF 0.9 that is 31.2 kW.
Does the formula work for 50 Hz and 60 Hz?
Yes. Frequency does not appear in the power equation; only voltage, current and power factor matter.