Wattage to Amperage Calculator — Watts to Amps
Calculate the current (amps) a device draws from its wattage and voltage. Supports DC, single-phase AC (with power factor), and three-phase AC circuits — useful for sizing fuses, breakers, and wiring.
W
V
Circuit type
Power factor
Amperes drawn at the given wattage and voltage
- 1
Effective denominator V × PF
120 × 1 = 120 - 2
Current I = P ÷ (V × PF)
1,200 ÷ 120 = 10
How does this calculator work?
Amps = Watts ÷ Volts for DC; divide by power factor for AC single-phase, and by (√3 × V × PF) for three-phase. Enter wattage, voltage, circuit type, and power factor to find the current drawn — essential for sizing fuses, cables, and breakers.
Formula
How this is calculated
Power (watts) is the product of voltage and current, with a correction for AC circuits called the power factor. For a DC circuit the relationship is simply P = V × I, so amps = watts ÷ volts. For single-phase AC, reactive components (motors, capacitors, inductors) cause the current to lead or lag the voltage; the power factor PF (between 0 and 1) accounts for this: I = P / (V × PF). Purely resistive loads (heaters, incandescent bulbs) have PF = 1.0 and the formula reduces to the DC case.
For three-phase circuits the line-to-line voltage (V) and the three-phase formula apply: P = √3 × V × I × PF, giving I = P / (√3 × V × PF). Enter the line-to-line voltage (e.g. 208 V or 415 V) for three-phase calculations.
The power factor depends on the load type. Resistive heaters and incandescent lights are 1.0; induction motors range 0.8–0.95; LED drivers and switch-mode power supplies are often 0.7–0.95. Always consult the equipment datasheet for the actual PF when sizing protective devices — using PF = 1 underestimates the current for reactive loads.
Frequently asked questions
Power factor (PF) is the ratio of real power (watts) to apparent power (volt-amps). A PF below 1 means the circuit draws more current than the watts alone suggest, because some current flows back and forth without doing useful work. Low PF increases wiring losses and trips breakers sooner.
An electric heater is a resistive load (PF = 1), so: I = 1500 W / 120 V = 12.5 A. It should be on a 15 A or 20 A circuit.
In a balanced three-phase system, the line-to-line voltage is √3 (≈ 1.732) times the phase voltage, and total power is √3 × V_LL × I × PF. This factor comes from the 120° phase offset between the three phases.
Also known as
TG we-Calculate Editorial Team. (2026). Wattage to Amperage Calculator — Watts to Amps [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/wattage-to-amperage-calculator
TG we-Calculate Editorial Team. "Wattage to Amperage Calculator — Watts to Amps." TG we-Calculate. 2026. https://we-calculate.com/calculator/wattage-to-amperage-calculator.
TG we-Calculate Editorial Team, "Wattage to Amperage Calculator — Watts to Amps," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/wattage-to-amperage-calculator
@misc{wecalculate_wattage_to_amperage_calculator, title = {Wattage to Amperage Calculator — Watts to Amps}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/wattage-to-amperage-calculator}}, year = {2026}, note = {TG we-Calculate} }
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