Amps to Watts Calculator
Your estimate
- Apparent power
- 1,800 VA1.8 kVA
- Continuous load (80 % rule)
- 1,440 W1.44 kW
How many watts a circuit or appliance uses from its amps and volts.
Updated 2026-10-20 · Based on: Ohm’s law, NEC Chapter 9 Table 8, 210.20 and 310.16; DIN VDE 0100-520 for metric.
How to use the Amps to Watts Calculator
- Enter the current in amps (from the label, a clamp meter or the breaker rating).
- Enter the voltage and choose single phase, three phase or DC.
- Enter the power factor for motors and electronics (1 for heaters and incandescent lights).
- Read the watts, the volt-amperes and how much a circuit of that size may carry continuously.
Formula
DC: watts = amps × volts. AC single phase: watts = amps × volts × power factor.
AC three phase: watts = √3 × amps × line-to-line volts × power factor.
Volt-amperes (VA) = volts × amps (× √3 on three phase) — what generators, UPS units and transformers are rated in.
Worked example
With the values preset in the calculator above:
- Current
- 15 A
- Voltage
- 120 V
- Phase
- Single phase
- Power factor (AC)
- 1
- Power
- 1,800 W (1.8 kW)
- Apparent power
- 1,800 VA (1.8 kVA)
- Continuous load (80 % rule)
- 1,440 W (1.44 kW)
How many watts is 15 or 20 amps?
- 15 A at 120 V = 1,800 W (continuous 1,440 W).
- 20 A at 120 V = 2,400 W (continuous 1,920 W).
- 30 A at 240 V = 7,200 W — a dryer or RV circuit.
- 50 A at 240 V = 12,000 W — a range or 50 A RV service.
- 10 A at 12 V DC = 120 W.
Watts, volts and amps explained
Volts are the electrical pressure, amps the flow and watts the work done per second. Multiply volts by amps and you get watts on DC and on purely resistive AC loads such as heaters, kettles and incandescent bulbs.
Motors, compressors and LED drivers draw some current that only flows back and forth. Their real power is lower than volts × amps; the ratio is the power factor, printed on many motor plates as “PF” or “cos φ”.
Amps to watts chart (120 V)
| Current | Power |
|---|---|
| 1 | 120 W |
| 5 | 600 W |
| 10 | 1,200 W |
| 15 | 1,800 W |
| 20 | 2,400 W |
| 30 | 3,600 W |
| 40 | 4,800 W |
| 50 | 6,000 W |
Frequently asked questions
How many watts is 15 amps at 120 volts?
1,800 W, or 1,440 W for a load that runs for three hours or more.
How many watts is 30 amps at 240 volts?
7,200 W.
How many watts is 1 amp?
120 W at 120 V, 240 W at 240 V and 12 W at 12 V DC.
Is VA the same as watts?
Only when the power factor is 1. A 1,000 VA UPS with a 0.6 power factor supports about 600 W.
More calculators
Estimates only — check quantities with your supplier and local building code before you order.