Amps to Watts Calculator
Convert amps to watts for DC, single-phase AC, and three-phase AC circuits. Get kilowatts, BTU/hr, wire gauge, breaker size, and monthly running cost.
A
Watts
—
Kilowatts —
BTU/hr —
Extended More scenarios, charts & detailed breakdown ▾
A
V
Power (W)
—
Kilowatts —
BTU/hr —
Apparent Power (VA) —
Professional Full parameters & maximum detail ▾
A
V
hrs
Power
Real Power (W) —
Apparent Power (VA) —
Reactive Power (VAR) —
Kilowatts (kW) —
BTU/hr —
Wiring & Cost
Recommended Wire Gauge —
Breaker Size —
Monthly Running Cost —
How to Use This Calculator
- Enter the amps (current).
- Select the voltage (120V or 240V for typical US circuits).
- Results show watts, kilowatts, and BTU/hr equivalent.
Formula
DC: P (W) = V × A
Single-phase AC: P (W) = V × A × PF
Three-phase AC: P (W) = V × A × √3 × PF
1 kW = 1,000 W | 1 kW = 3,412 BTU/hr
Example
Example: 10 A, 120 V, PF = 0.9 → Real power = 1,080 W (1.08 kW) → 3,685 BTU/hr.
Frequently Asked Questions
- For DC circuits: Watts = Amps × Volts. For single-phase AC: Watts = Amps × Volts × Power Factor. For three-phase AC: Watts = Amps × Volts × √3 × Power Factor.
- Power factor (PF) is the ratio of real power (watts) to apparent power (volt-amps). Resistive loads like heaters have PF = 1.0. Motors and some electronics typically have PF = 0.8–0.95.
- Watts (W) measure real power consumed. Volt-amps (VA) measure apparent power. For resistive loads they are equal; for reactive loads (motors, transformers), VA > W.
- 15 amps × 120 volts = 1,800 watts (for a resistive DC or AC circuit with PF=1). With a typical AC power factor of 0.9, that is 1,620 watts of real power.
- A 15A circuit typically uses 14 AWG wire. A 20A circuit uses 12 AWG. A 30A circuit uses 10 AWG. Always consult the NEC and a licensed electrician for your installation.