How to use the watts to amps converter
- Enter the power in watts.
- Enter the voltage of the circuit in volts.
- Select the circuit type: DC, AC single-phase or AC three-phase.
- For AC circuits, enter the power factor (0 to 1). Leave at 1 for purely resistive loads.
- Read the resulting current in amps below.
Formulas used for watts to amps conversion
The relationship between power, voltage and current depends on the type of circuit. For direct current (DC), the formula is straightforward:
I = P / V
where I is current in amps, P is power in watts and V is voltage in volts. For example, a 1500 W heater on a 120 V DC circuit draws 1500 / 120 = 12.5 A.
For alternating current (AC) single-phase circuits, you must account for the power factor (PF):
I = P / (V x PF)
A 2000 W motor on 240 V single-phase with a power factor of 0.85 draws 2000 / (240 x 0.85) = 9.80 A.
For AC three-phase systems using line-to-line voltage, the square root of 3 (approximately 1.732) enters the equation:
I = P / (sqrt(3) x V x PF)
A 10,000 W load on 480 V three-phase at 0.9 PF draws 10000 / (1.73205 x 480 x 0.9) = 13.36 A.
Common watts to amps reference table
This table shows current draw for typical wattages at 120 V DC (or single-phase AC at a power factor of 1). For single-phase AC, divide these values by your power factor; three-phase uses a different formula.
| Power (W) | Voltage (V) | Current (A) DC |
|---|---|---|
| 60 | 120 | 0.5 |
| 100 | 120 | 0.833 |
| 500 | 120 | 4.167 |
| 1000 | 120 | 8.333 |
| 1500 | 120 | 12.5 |
| 2000 | 120 | 16.667 |
| 3000 | 120 | 25 |
Reversing the calculation: amps to watts
You can use the same relationships to go from amps to watts. Multiply current by voltage for DC: P = I x V. For single-phase AC, multiply by the power factor as well: P = I x V x PF. For three-phase AC: P = I x sqrt(3) x V x PF. If you know a device draws 10 A on a 240 V single-phase circuit with a 0.9 power factor, its real power consumption is 10 x 240 x 0.9 = 2160 W.
Understanding power factor
Power factor is the ratio of real power (watts) to apparent power (volt-amps). It ranges from 0 to 1. A purely resistive load like an incandescent bulb or electric heater has a power factor of 1. Inductive loads such as motors, transformers and compressors have a power factor less than 1, typically between 0.7 and 0.9. A lower power factor means more current is required to deliver the same amount of real power. This is why industrial facilities install capacitor banks to correct power factor and reduce current draw on their wiring.
Practical applications
Converting watts to amps is essential when sizing circuit breakers and selecting wire gauges. The National Electrical Code (NEC) requires that continuous loads not exceed 80 percent of a breaker rating. A 1500 W heater on a 120 V circuit draws 12.5 A, which exceeds 80 percent of a 15 A breaker (12 A), so a 20 A circuit is needed if the heater runs continuously. Knowing the current also helps when planning solar panel arrays, sizing inverters and calculating energy costs. For related electrical calculations, you may also need an ohms law calculator to find resistance, or a voltage drop calculator to check long wire runs. Once you have the current, a wire size calculator helps select the correct conductor.
Worked examples
| Example | Input | Result |
|---|---|---|
| 1500 W space heater on 120 V DC | Power (watts): 1500; Voltage (V): 120; Circuit type: dc; Power factor: 1 | Current: 12.5 A; Formula: I = P / V; Circuit type: DC; Power: 1,500 W; Voltage: 120 V |
| 2000 W motor on 240 V single-phase, PF 0.85 | Power (watts): 2000; Voltage (V): 240; Circuit type: ac1; Power factor: 0.85 | Current: 9.803922 A; Formula: I = P / (V × PF); Circuit type: AC single-phase; Power: 2,000 W; Voltage: 240 V; Power factor: 0.85 |
| 10 kW load on 480 V three-phase, PF 0.9 | Power (watts): 10000; Voltage (V): 480; Circuit type: ac3; Power factor: 0.9 | Current: 13.36459 A; Formula: I = P / (√3 × V × PF); Circuit type: AC three-phase; Power: 10,000 W; Voltage: 480 V; Power factor: 0.9 |
| 60 W LED bulb on 120 V single-phase, PF 0.95 | Power (watts): 60; Voltage (V): 120; Circuit type: ac1; Power factor: 0.95 | Current: 0.526316 A; Formula: I = P / (V × PF); Circuit type: AC single-phase; Power: 60 W; Voltage: 120 V; Power factor: 0.95 |
FAQ
How do I convert watts to amps?
Divide the power in watts by the voltage in volts for DC circuits. For AC circuits, also divide by the power factor. For three-phase AC, divide by the square root of 3 as well.
How many amps is 1500 watts at 120 volts?
For a DC or purely resistive AC circuit, 1500 W divided by 120 V equals 12.5 A.
What is power factor and why does it matter?
Power factor measures how effectively electrical power is converted into useful work. A lower power factor means higher current is needed for the same wattage, which affects wire sizing and breaker selection.
Can I use this tool to convert amps to watts?
Not directly. This tool converts watts to amps only. To go the other way, multiply amps by volts (and by power factor for AC) to get watts.
Why does three-phase power use the square root of 3?
In a balanced three-phase system, the line-to-line voltage is the square root of 3 times the phase voltage. This geometric relationship comes from the 120-degree phase separation between the three conductors.
Is this converter safe to use for electrical planning?
The math is accurate, but always consult local electrical codes and a qualified electrician for real installations. Breaker sizing, derating factors and ambient temperature all affect safe design.