Amps to Watts Calculator
Converting amps to watts tells you how much power a circuit can deliver or how much power a load is consuming. This is especially important when sizing circuits, verifying panel capacity, and calculating electrical loads for service entrance calculations. Every electrician needs this conversion when working with equipment rated in amps but billing or load calculations require watts.
The formula is the reverse of the watts-to-amps conversion. You multiply the current in amps by the voltage to get power in watts. For a standard 20-amp, 120-volt branch circuit, the maximum power available is 2,400 watts. Applying the NEC 80% rule for continuous loads, the safe working capacity drops to 1,920 watts.
This calculation is critical for load balancing in electrical panels. When adding new circuits or appliances, electricians must verify the total connected load in watts does not exceed the panel's amperage rating multiplied by the service voltage. For a 200-amp, 240-volt residential service, the theoretical maximum is 48,000 watts (200 × 240).
Amps to Watts Formula
Watts = Amps × Volts
For DC and single-phase AC circuits
Circuit Capacity by Breaker Size
| Breaker (Amps) | 120V Watts | 240V Watts | 80% Continuous (120V) |
|---|---|---|---|
| 15 A | 1,800 W | 3,600 W | 1,440 W |
| 20 A | 2,400 W | 4,800 W | 1,920 W |
| 30 A | 3,600 W | 7,200 W | 2,880 W |
| 40 A | 4,800 W | 9,600 W | 3,840 W |
| 50 A | 6,000 W | 12,000 W | 4,800 W |
| 60 A | 7,200 W | 14,400 W | 5,760 W |
How to Use This Calculator
- Enter the amperage — the current draw or circuit breaker rating in amps.
- Enter the voltage — defaults to 120V. Change to 240V for double-pole circuits or other voltages as needed.
- Read the result — the wattage is calculated instantly.
Frequently Asked Questions
How do you convert amps to watts?
To convert amps to watts, multiply the amperage by the voltage. The formula is: Watts = Amps x Volts. For example, a 20-amp circuit at 120 volts provides 2,400 watts of power (20 x 120 = 2,400).
How many watts is a 20-amp 240-volt circuit?
A 20-amp circuit at 240 volts provides 4,800 watts of power (20 x 240 = 4,800). However, per the NEC 80% continuous load rule, the safe continuous capacity is 3,840 watts (4,800 x 0.80).
What is the difference between watts and amps?
Watts measure power (the rate of energy use), while amps measure current (the flow of electrons through a conductor). They are related by voltage: Watts = Amps x Volts. A circuit breaker trips based on amps, but your electric bill is based on watts (kilowatt-hours).