Calculator
Watts to Amps Calculator
Convert between watts, amps, and volts for DC, single-phase, and three-phase AC circuits. Pick what to solve for, enter the load and voltage, set power factor for motors, and get the amperage that matches the real circuit. Free, no signup.
Free
Solve for
Single-phase ACPF 1
Current (I)12.5 A
I = P ÷ (V × PF)
Real power
1,500 WTrue power doing work (W)
Apparent power
1,500 VAS = V × I
Voltage
120 V
Current
12.5 A
What you'll get
Pick circuit type and what to solve for
Choose DC, single-phase, or three-phase, then solve for amps, watts, or volts. Three-phase automatically applies the √3 line-to-line factor.
Enter the load and set power factor
Enter the two known values, for example watts and volts, and set power factor for AC (1.0 for resistive heaters, about 0.85 for motors). DC ignores power factor.
Read amps plus apparent power
Get the solved value with the exact formula used, plus real power (W), apparent power (VA), and reactive power so you can size breakers, wire, and generators correctly.
How it works
- 1
Pick circuit type and what to solve for
Choose DC, single-phase, or three-phase, then solve for amps, watts, or volts. Three-phase automatically applies the √3 line-to-line factor.
- 2
Enter the load and set power factor
Enter the two known values, for example watts and volts, and set power factor for AC (1.0 for resistive heaters, about 0.85 for motors). DC ignores power factor.
- 3
Read amps plus apparent power
Get the solved value with the exact formula used, plus real power (W), apparent power (VA), and reactive power so you can size breakers, wire, and generators correctly.
Converting watts, amps, and volts the right way
On a DC or purely resistive circuit, watts, amps, and volts follow the simple power law P = V × I, so amps equal watts divided by volts. But most real electrical loads are AC, and two things change the math: power factor and phase. Power factor (PF) is the fraction of supplied power that does real work, 1.0 for resistive loads like heaters, and roughly 0.8 to 0.9 for induction motors, so single-phase current is I = P ÷ (V × PF). Three-phase circuits add the √3 (about 1.732) factor for line-to-line voltage, giving I = P ÷ (√3 × V × PF).
This calculator handles all three cases. To convert 2,000 watts at 240 V single-phase with a 0.8 power factor, it returns about 10.4 amps; the same 2,000 watts at unity power factor returns 8.33 amps. Switch to three-phase for a 10 kW load at 400 V and 0.8 PF and you get about 18 amps. Because it also reports apparent power in volt-amps (VA), it is useful for sizing generators, transformers, and UPS units, not just breakers and conductors. Pair it with the wire size and voltage drop calculators to take a load from watts all the way to a correctly sized, code-compliant circuit.
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Watts to Amps Calculator FAQs
For DC or resistive loads, amps = watts ÷ volts. For single-phase AC, amps = watts ÷ (volts × power factor). For three-phase AC, amps = watts ÷ (√3 × volts × power factor), where √3 ≈ 1.732 and volts is line-to-line. This calculator applies the right formula automatically once you pick the circuit type.
Use 1.0 for resistive loads such as electric heaters, incandescent lighting, and baseboard heat. Use about 0.85 for typical induction motors at full load, and roughly 0.9 for mixed commercial loads. When in doubt, check the equipment nameplate, it often lists the power factor directly.
The √3 formula used here takes line-to-line voltage, for example 208 V, 240 V, or 480 V between phases. That is the voltage marked on most three-phase equipment. If you only have line-to-neutral voltage, multiply it by √3 to get line-to-line first.
Watts are real power, the power actually doing work. Volt-amps are apparent power, voltage times current before power factor. They are equal only when power factor is 1. Generators, transformers, and UPS units are rated in VA, so this calculator reports both so you can size that equipment correctly.
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