Watts to Amps Calculator
Convert watts to amps for DC, single-phase AC and three-phase AC circuits, using the voltage and power factor, with a table of common voltages.
Results
| Item | Value |
|---|
Current at common voltages
| Voltage | Amps |
|---|
Quick Answer
Amps = watts ÷ volts for DC and simple AC loads. A 1,500 watt space heater on 120 volts draws 12.5 amps. For three-phase power, amps = watts ÷ (1.732 × volts × power factor), so a 10,000 W motor at 480 V with a 0.85 power factor draws about 14.2 amps.
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Table of Contents
- Watts to Amps Calculator
- Quick Answer
- Related Calculators
- How This Watts to Amps Calculator Works
- How to Use the Watts to Amps Calculator
- Core Formulas
- Key Terms
- Worked Example
- Real-Life Examples
- Watts vs Amps vs Volts
- Common Appliance Currents at 120 V
- Common Mistakes to Avoid
- Frequently Asked Questions
- References & Sources
How This Watts to Amps Calculator Works
Enter the power in watts, the voltage and the type of circuit. For AC circuits, enter the power factor from the device’s nameplate, or 1 for heaters and other resistive loads. The calculator divides power by voltage (and by power factor and √3 where needed) to give the current in amps, and lists the current at other common voltages.
Quick explanation: the same power draws fewer amps at a higher voltage.
- DC: amps = watts ÷ volts.
- AC single-phase: divide also by the power factor.
- AC three-phase: divide also by √3 (1.732).
How to Use the Watts to Amps Calculator
- Enter the power in watts from the device label.
- Enter the voltage.
- Choose DC, AC single-phase or AC three-phase.
- For AC, enter the power factor, or 1 if unknown for heaters.
- Press Calculate and read the current in amps.
Core Formulas
- DC: I = P ÷ V
- AC single-phase: I = P ÷ (PF × V)
- AC three-phase: I = P ÷ (√3 × PF × VL-L)
I is current in amps, P is real power in watts, V is voltage and PF is power factor.
Key Terms
- Watt: a unit of power, one joule per second.
- Amp: a unit of electric current.
- Volt: a unit of electrical potential difference.
- Power factor: the ratio of real power to apparent power in AC circuits, from 0 to 1.
- Three-phase: power delivered on three alternating currents, common in commercial buildings.
Worked Example
A 10 kW three-phase motor runs at 480 V with a power factor of 0.85.
- I = 10,000 ÷ (1.732 × 0.85 × 480)
- I = 10,000 ÷ 706.7
- I = 14.15 amps
Real-Life Examples
- Space heater: 1,500 W at 120 V draws 12.5 A, a large share of a 15 A circuit.
- EV charger: 7,680 W at 240 V draws 32 A.
- 12 V system: a 120 W fridge on 12 V DC draws 10 A.
- Motor: 5,000 W single-phase at 230 V with PF 0.8 draws 27.2 A.
Watts vs Amps vs Volts
- Watts: the rate of energy use, or power.
- Amps: the flow of electric current.
- Volts: the electrical pressure that pushes current.
- Link: watts = volts × amps (× power factor for AC).
Common Appliance Currents at 120 V
Wattages are typical examples. Check your device’s label.
| Device | Watts | Amps |
|---|---|---|
| LED bulb | 10 | 0.1 |
| Laptop charger | 65 | 0.5 |
| Television | 150 | 1.2 |
| Microwave | 1,100 | 9.2 |
| Hair dryer | 1,500 | 12.5 |
| Space heater | 1,500 | 12.5 |
| Toaster oven | 1,800 | 15.0 |
Common Mistakes to Avoid
- Ignoring power factor. Motors draw more current than watts ÷ volts suggests.
- Using phase voltage for three-phase. Use the line-to-line voltage.
- Loading a breaker to 100%. Continuous loads should stay at or below 80% of the rating.
- Using peak watts. Use the running watts for steady current.
- Mixing kW and W. 1 kW = 1,000 W.
Frequently Asked Questions
Divide watts by volts. For AC, also divide by the power factor, and for three-phase, by 1.732.
12.5 amps at 120 V, or 6.25 amps at 240 V.
About 8.3 amps.
15 × 120 = 1,800 W, or about 1,440 W for continuous loads at 80%.
1 for heaters and incandescent lights. Motors often run around 0.8 to 0.9. Check the nameplate.
Power is shared across three wires, so each carries less current.
The same power draws half the current at 240 V, which can allow smaller wire.
Multiply amps by volts (and by power factor for AC).
VA is apparent power. Watts are real power. Watts = VA × power factor.
Yes. Choose DC and enter the battery or panel voltage.
It depends on the load, wire and code. A licensed electrician should size it.
Divide its watts by 12. A 60 W device uses 5 A.
Check the label. Many home fridges use around 100 to 250 W while running, which is roughly 1 to 2 amps at 120 V, but they can briefly draw more when the compressor starts.
Labels often list the maximum or starting current, and AC devices with a power factor below 1 draw more amps than watts ÷ volts. Use the label’s running watts and power factor for the steadiest estimate.
Find the amps with this calculator, then choose a cord rated above that current. Long cords need thicker wire, and our Voltage Drop Calculator shows how length affects voltage.
Homes usually have single-phase power at 120 or 240 V. Factories and large buildings often use three-phase power, which runs motors more smoothly and carries more power on each wire.
References & Sources
| Source | Used For | Link |
|---|---|---|
| Wikipedia, Electric power | Power, voltage and current. | https://en.wikipedia.org/wiki/Electric_power |
| Wikipedia, Power factor | Real and apparent power in AC circuits. | https://en.wikipedia.org/wiki/Power_factor |