Watts to Amps Calculator
Convert watts to amps, or amps to watts, for DC, single-phase AC and three-phase AC circuits. The calculator also suggests a minimum breaker size, which is useful when you check whether a generator outlet or circuit can handle a load.
Watts to Amps Calculator
Convert watts to amps, or amps to watts, for DC, single-phase AC and three-phase AC circuits.
Breaker suggestions follow the common rule that continuous loads should not exceed 80% of a breaker's rating. They are a starting point, not a code determination.
Watts to amps formulas
| Circuit | Watts → amps | Amps → watts |
|---|---|---|
| DC | I = P ÷ V | P = I × V |
| AC single-phase | I = P ÷ (V × PF) | P = I × V × PF |
| AC three-phase (line-to-line voltage) | I = P ÷ (√3 × V × PF) | P = √3 × I × V × PF |
Where P is real power in watts, I is current in amps, V is voltage, PF is power factor and √3 ≈ 1.732.
Examples
- A 1,800 W space heater on 120 V: 1,800 ÷ 120 = 15 A. A heater is a continuous load, so 15 ÷ 0.8 = 18.75 A and it belongs on a 20 A circuit, not a 15 A one.
- A 7,200 W load on a 240 V generator outlet: 7,200 ÷ 240 = 30 A, the full rating of an L14-30 outlet.
- A 10 kW three-phase load at 208 V and 0.8 PF: 10,000 ÷ (1.732 × 208 × 0.8) = 34.7 A per phase.
Watts to amps at common voltages
| Watts | 12 V DC | 120 V AC | 240 V AC |
|---|---|---|---|
| 100 W | 8.33 A | 0.83 A | 0.42 A |
| 500 W | 41.7 A | 4.17 A | 2.08 A |
| 1,000 W | 83.3 A | 8.33 A | 4.17 A |
| 1,500 W | 125 A | 12.5 A | 6.25 A |
| 2,000 W | 167 A | 16.7 A | 8.33 A |
| 3,600 W | 300 A | 30 A | 15 A |
| 5,000 W | 417 A | 41.7 A | 20.8 A |
| 7,500 W | 625 A | 62.5 A | 31.3 A |
| 10,000 W | 833 A | 83.3 A | 41.7 A |
AC values assume a power factor of 1.0. The 12 V column shows why large inverters need very heavy cables.
What is power factor?
In AC circuits, motors and some electronics draw current that is slightly out of step with the voltage. Power factor (0 to 1) is the share of that current doing useful work. Resistive loads such as heaters and incandescent lights have a PF of 1.0. Induction motors typically run at 0.8 to 0.9, and modern electronics with power-factor correction at 0.95 or higher. A lower power factor means more amps for the same watts. See the kVA to kW calculator for more.
About the breaker suggestion
Loads that run for three hours or more are considered continuous, and a common rule is that they should not exceed 80% of the breaker rating. The calculator divides your current by 0.8 and picks the next standard breaker size. Wire must also be rated for the breaker. Check with the wire size calculator, and have an electrician confirm any new circuit.
Frequently asked questions
How many amps is a 3,500 W generator?
At 120 V, 3,500 ÷ 120 = 29.2 A total across its outlets. Each standard 20 A outlet is still limited by its own breaker, so one outlet cannot deliver the full output.
How many watts can a 20 amp circuit handle?
20 A × 120 V = 2,400 W maximum, or 1,920 W for continuous loads at 80%.