How to use the watts to amps calculator
- Choose DC, AC single-phase (homes) or AC three-phase (commercial and industrial).
- Enter the power in watts, kilowatts or horsepower — from the appliance label or nameplate.
- Enter the voltage. For three-phase, use the line-to-line voltage.
- For AC, enter the power factor (1 for heaters; 0.8–0.95 for motors).
Watts to amps formulas
DC: I = P ÷ V AC single-phase: I = P ÷ (V × PF) AC three-phase: I = P ÷ (√3 × V(L-L) × PF) 1 hp = 745.7 W · 1 kW = 1,000 W
Worked examples
- Space heater: 1,500 W at 120 V → 1,500 ÷ 120 = 12.5 A.
- Kettle in India or the UK: 2,000 W at 230 V → 8.7 A.
- Motor: 1 hp (746 W) at 230 V with PF 0.8 → 746 ÷ (230 × 0.8) = 4.05 A.
- Three-phase load: 10 kW at 400 V, PF 0.85 → 10,000 ÷ (1.732 × 400 × 0.85) = 17.0 A.
- 12 V system: 600 W ÷ 12 V = 50 A.
Watts to amps chart
| Watts | 12 V DC | 120 V | 230 V | 240 V |
|---|---|---|---|---|
| 100 W | 8.33 A | 0.83 A | 0.43 A | 0.42 A |
| 500 W | 41.7 A | 4.17 A | 2.17 A | 2.08 A |
| 1,000 W | 83.3 A | 8.33 A | 4.35 A | 4.17 A |
| 1,500 W | 125 A | 12.5 A | 6.52 A | 6.25 A |
| 2,000 W | 167 A | 16.7 A | 8.70 A | 8.33 A |
| 3,000 W | 250 A | 25.0 A | 13.0 A | 12.5 A |
| 5,000 W | 417 A | 41.7 A | 21.7 A | 20.8 A |
Chart assumes a power factor of 1 (resistive load).
Why voltage matters
For the same power, higher voltage means lower current. That is why big appliances such as dryers, EV chargers and water heaters in the US use 240 V instead of 120 V: half the current means thinner wire and less heat. It is also why low-voltage 12 V systems need very thick cables — a 1,000 W load at 12 V draws over 80 A.
Going the other way: amps to watts
Rearrange the same formulas: watts = amps × volts for DC, watts = amps × volts × power factor for single-phase AC, and watts = 1.732 × amps × volts × power factor for three-phase. A 15 A, 120 V household circuit can supply up to 1,800 W, or 1,440 W for a continuous load at 80%.
Safety notes
- Use the appliance’s rated watts. Motors can draw 3–7 times their running current for a moment when starting.
- Circuits for continuous loads (3+ hours) are usually sized at 125% of the load current.
- Electrical work is regulated in most countries. Use a licensed electrician for new circuits.