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Watts ↔ amps calculator
Convert watts to amps or amps to watts for DC, single-phase AC and three-phase AC circuits at any voltage and power factor.
Results
| Current | 12.5 A |
|---|---|
| Apparent power | 1,500 VA |
- Household circuits: a 15 A, 120 V circuit should carry no more than about 12 A (1,440 W) continuously. A 20 A circuit should carry about 16 A (1,920 W).
About this calculator
Watts measure power and amps measure current, and voltage links the two. The same 1,500 W heater draws 12.5 A on a 120 V outlet, 6.25 A at 240 V and 125 A from a 12 V battery through an inverter (more once you add inverter losses). That's why the same appliance can be trivial for a wall socket and a serious engineering problem in a van.
This converter handles DC, single-phase AC and three-phase AC, including power factor for motors and electronics.
How to use it
- Choose watts → amps or amps → watts.
- Pick the circuit type. Use DC for batteries and solar, single-phase for normal household outlets, and three-phase for commercial equipment.
- Enter the voltage: 120 V or 240 V for US homes, 230 V for most of Europe, or the battery's nominal voltage.
- For AC motors and electronics, enter the power factor from the nameplate if listed.
The formula
DC: I = P ÷ V.
AC single-phase: I = P ÷ (V × PF).
AC three-phase: I = P ÷ (√3 × VL-L × PF).
Apparent power (VA) = V × I (× √3 for three-phase). Real power (W) = VA × PF.
Worked example (default values)
Inputs
| Convert | Watts → amps |
|---|---|
| Circuit | AC single-phase |
| Watts or amps | 1500 W or A |
| Voltage | 120 V |
| Power factor (AC) | 1 |
Results
| Current | 12.5 A |
|---|---|
| Apparent power | 1,500 VA |
Tips and common mistakes
Inverter loads on batteries: to find the battery current, divide watts by battery voltage and inverter efficiency, e.g. 1,500 W ÷ (12 V × 0.9) ≈ 139 A. The inverter size calculator does this for a whole appliance list.
UPS and inverter ratings in VA are higher than their watt ratings. A "1500 VA" UPS might only supply 900 W.
Frequently asked questions
How many amps is 1500 watts?
12.5 A at 120 V, 6.25 A at 240 V and 125 A at 12 V DC (before inverter losses).
How many watts can a 15 amp circuit handle?
1,800 W at 120 V peak, but only about 1,440 W continuously (80% rule).
What is power factor?
The ratio of real power to apparent power in AC circuits. Motors and some electronics draw current that's out of step with voltage, so they need more amps for the same watts.
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Estimates for planning only, based on the assumptions shown. Real-world performance varies with equipment, temperature and installation. Updated October 19, 2026. See our methodology.