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Equipment estimate only. Verify voltage, load profile, losses, duty cycle, manufacturer specifications, and electrical safety requirements before relying on the result.
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What does this calculator estimate?
Convert watts to amps for DC, single-phase AC, or three-phase AC. Enter power, voltage, system type, and power factor to get current in amps — the reverse of a volts-and-amps wattage calculation, entirely in your browser.
- Amps = watts ÷ volts (DC).
- Single-phase AC: amps = watts ÷ (volts × power factor).
- Three-phase AC: amps = watts ÷ (√3 × volts × power factor).
Watts, volts, and amps in practice
Watts measure power, volts measure electrical pressure, and amps measure current flow. They are linked by the relationship watts = volts × amps (for DC), so converting any two gives the third. This calculator takes watts and voltage and returns the current, handling the AC power-factor and phase differences automatically.
Common household loads
A typical 120 V household circuit is rated 15 A (1,800 W) or 20 A (2,400 W). Space heaters (1,500 W), hair dryers (1,800 W), and microwaves (1,000 W) are among the heaviest loads — a 1,500 W heater on a 15 A circuit draws 12.5 A, already close to the limit. Larger appliances like dryers and EV chargers use 240 V circuits.
Why three-phase differs
Three-phase power delivers energy more efficiently because the three waveforms overlap, so the current for a given wattage is lower: divide by √3 (about 1.732) instead of the single-phase factor. That is why industrial equipment running on three-phase needs smaller conductors for the same power.
How this calculator works
Formula
Current (A) = power (W) ÷ voltage-adjusted factor. DC: factor = voltage. Single-phase AC: factor = voltage × power factor. Three-phase AC: factor = √3 × voltage × power factor.
Worked example
A 1,500 W space heater on 120 V single-phase AC with power factor 1 draws 1,500 ÷ 120 = 12.5 A. The same load on three-phase with a 0.9 power factor draws about 1,500 ÷ (1.732 × 120 × 0.9) = 8.0 A.
Assumptions to verify
- AC power factor is assumed where selected; DC ignores it.
- Nameplate watts may differ from actual draw under load.
- This estimate does not size conductors, breakers, or equipment.
Frequently asked questions
How do I convert watts to amps?
Divide watts by volts: amps = watts ÷ volts. For single-phase AC, divide by volts × power factor; for three-phase, divide by √3 × volts × power factor. A 1,500 W heater on 120 V single-phase draws 12.5 A.
What is the difference between DC, single-phase, and three-phase?
DC (direct current) is battery/solar power where amps = watts ÷ volts. Single-phase AC is standard household power in North America. Three-phase AC is industrial/commercial power and uses the √3 factor because the phases deliver power simultaneously.
Why does power factor matter?
Power factor (0 to 1) measures how effectively an AC load uses the supplied current. Motors and some electronics have a power factor below 1, drawing more current than watts ÷ volts alone would suggest. Entering the correct factor gives a more accurate current.
Can I size a breaker from watts to amps?
Use the amps as a starting point, but never size breakers or conductors from this estimate alone. Qualified electrical design must account for code, derating, motor inrush, and continuous-load rules. Consult a licensed electrician.
Cite this tool
BoringToolsKit. “Watts to Amps Calculator.” boringtoolskit.com/watts-to-amps-calculator/ (reviewed August 2026). Free to reference in articles, syllabi, and answer posts with a link.
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