About the Amps to Watts Converter
This amps to watts converter works out how much power a circuit or appliance draws from its current. Enter the current in amps, pick DC, single-phase AC or three-phase AC, type the voltage and (for AC) the power factor, and you get real power in watts and kilowatts, plus apparent power in volt-amps for AC loads.
Use it to check what a 15 A or 20 A household circuit can deliver, to size a generator, inverter or UPS from a nameplate current, to estimate a motor or heater's power from a clamp-meter reading, or to convert 12 V battery currents into watts for solar and RV setups.
Amps alone cannot be turned into watts — you always need the voltage. For three-phase systems enter the line-to-line voltage (for example 208, 400 or 480 V). Resistive loads such as kettles and heaters have a power factor of 1; motors and many electronics are lower, often 0.8–0.95.
With the default inputs, the real power is 1,200 W. Change any value above to recalculate instantly.
How to use the amps to watts converter
- 1Enter the current in amps from the nameplate or a clamp meter.
- 2Choose DC, single-phase AC or three-phase AC.
- 3Enter the voltage (line-to-line for three-phase).
- 4For AC, enter the power factor — use 1 if unsure and the load is resistive.
- 5Read the watts, kilowatts and apparent power (VA).
Formula and method
Electrical power is voltage multiplied by current. For direct current that is the whole story: 12 V × 5 A = 60 W. For alternating current the voltage and current can be out of step, so real power (watts) is apparent power (volt-amps) multiplied by the power factor, a number between 0 and 1.
Balanced three-phase circuits carry power on three conductors, so with the line-to-line voltage the formula gains a factor of √3 ≈ 1.732. If you only know the line-to-neutral voltage, multiply it by √3 first (for example 277 V × 1.732 ≈ 480 V). Horsepower uses 1 hp = 745.7 W (mechanical horsepower).
- P
- Real power in watts (W)
- V
- Voltage in volts (line-to-line for three-phase)
- I
- Current in amps (A)
- PF
- Power factor, 0 to 1 (1 for DC and resistive loads)
Worked examples
10 A on a 120 V household circuit
A resistive load has a power factor of 1, so P = 120 V × 10 A × 1 = 1,200 W, or 1.2 kW.
Three-phase motor: 20 A at 480 V, PF 0.85
Apparent power is 1.732 × 480 × 20 = 16,628 VA. Multiplying by the 0.85 power factor gives about 14,134 W (14.1 kW) of real power.
5 A from a 12 V battery
DC has no power factor, so P = 12 V × 5 A = 60 W.
Frequently asked questions
How many watts is 15 amps?+
At 120 V, 15 A is 1,800 W (120 × 15). At 230 V it is 3,450 W and at 240 V it is 3,600 W, assuming a resistive load with power factor 1.
How many watts is 20 amps at 240 volts?+
20 A × 240 V = 4,800 W for a resistive single-phase load. For a motor with a power factor of 0.9 the real power would be about 4,320 W.
Can I convert amps to watts without voltage?+
No. Watts equal volts times amps, so the same 10 A is 120 W at 12 V but 1,200 W at 120 V. Check the device label or the supply voltage first.
What is power factor?+
Power factor is the ratio of real power (W) to apparent power (VA) in an AC circuit. Heaters and incandescent lamps are close to 1; induction motors are typically 0.8–0.9 at full load.
Why is there a √3 in the three-phase formula?+
In a balanced three-phase system the line-to-line voltage is √3 times the phase voltage, and total power across the three phases works out to √3 × V(L-L) × I × PF.