About the Watts to Amps Converter
This watts to amps converter tells you how much current a load pulls from its power rating. Enter the wattage, choose DC, single-phase AC or three-phase AC, set the voltage and, for AC, the power factor, and it returns the current in amps along with the apparent power in kVA.
It is useful when checking whether a space heater, kettle or air conditioner will fit on a 15 A or 20 A circuit, choosing a fuse or cable for a 12 V or 24 V DC system, sizing an inverter for an RV or boat, or estimating motor current on a 208, 400 or 480 V three-phase supply.
For three-phase circuits enter the line-to-line voltage. The tool also shows 125% of the current, the figure commonly used when a load runs continuously for three hours or more. It is an estimate for planning — follow your local electrical code and a licensed electrician for actual wiring and breaker choices.
With the default inputs, the current is 12.5 A. Change any value above to recalculate instantly.
How to use the watts to amps converter
- 1Enter the power rating in watts from the label or spec sheet.
- 2Choose DC, single-phase AC or three-phase AC.
- 3Enter the supply voltage (line-to-line for three-phase).
- 4For AC, enter the power factor — 1 for heaters, about 0.85 for motors.
- 5Read the current and the 125% continuous-load figure.
Formula and method
Current is power divided by voltage. In AC circuits only part of the apparent power does useful work, so the real power in watts is divided by the power factor as well — a lower power factor means more current for the same wattage.
In a balanced three-phase system the line current is the power divided by √3 (≈ 1.732) times the line-to-line voltage times the power factor. Apparent power is P ÷ PF. The 125% figure multiplies the current by 1.25, the usual allowance for continuous loads when sizing conductors and overcurrent devices.
- I
- Current in amps (A)
- P
- Real power in watts (W)
- V
- Voltage in volts (line-to-line for three-phase)
- PF
- Power factor, 0 to 1 (1 for DC and resistive loads)
Worked examples
1,500 W space heater on 120 V
I = 1,500 ÷ 120 = 12.5 A. Sized as a continuous load, 125% of that is 15.6 A — already above the rating of a 15 A circuit, which is why 1,500 W is the practical ceiling for plug-in heaters and one running for hours is best on a 20 A or dedicated circuit.
10 kW three-phase motor at 400 V, PF 0.9
I = 10,000 ÷ (1.732 × 400 × 0.9) = 10,000 ÷ 623.5 ≈ 16.04 A. Apparent power is 10 ÷ 0.9 = 11.1 kVA.
100 W device on a 12 V battery
For DC, I = 100 ÷ 12 = 8.33 A — ten times the 0.83 A the same 100 W draws at 120 V AC, which is why low-voltage systems need thicker cable.
Frequently asked questions
How many amps is 1500 watts?+
1,500 W draws 12.5 A at 120 V, 6.25 A at 240 V and about 6.5 A at 230 V, assuming a resistive load such as a heater with power factor 1.
How many amps does a 2000 watt appliance use?+
At 120 V a 2,000 W appliance uses 16.7 A, more than a standard 15 A circuit allows. At 230 V it uses about 8.7 A and at 240 V about 8.3 A.
How do I convert watts to amps for three-phase?+
Divide the power by √3 × line-to-line voltage × power factor. For example, 10 kW at 400 V and PF 0.9 is 10,000 ÷ (1.732 × 400 × 0.9) ≈ 16 A per line.
Why multiply by 125% for continuous loads?+
Loads that run three hours or more are commonly sized at 125% of their current, so the circuit runs at no more than 80% of its rating. A 15 A circuit therefore carries about 12 A continuously.
Do I need the power factor for watts to amps?+
Only for AC. Motors, compressors and some electronics have power factors below 1, which raises the current. If you leave it at 1 for such loads, you will underestimate the amps.