Amps = watts ÷ volts for DC or single-phase AC at power factor 1. For other AC loads include power factor; for balanced three-phase loads also include √3 and use line-to-line voltage. Enter electrical input watts, or select motor shaft output and supply efficiency.
Watts to amps calculator
0.90 means 90%. Use an efficiency appropriate to the operating load.
Use the actual voltage across the load; for AC, use RMS voltage.
Decimal point or comma accepted: 1500.5 or 1500,5. Write thousands without separators. PF and efficiency must be greater than 0 and no more than 1.
1500 W ÷ (120 V × 1 PF) = 12.5 A
1500 W is electrical input power. Efficiency is not applied again.
This estimates operating current. It does not select a circuit breaker or conductor, calculate motor starting current, or establish that an appliance can use a different voltage.
Compare current at ten voltages
| Voltage | Calculated current |
|---|
Compare up to three cases
Save a result, change your inputs, then save again. Cases remain only during this page visit. Reset inputs keeps saved cases; Clear saved cases removes them.
| Case | Entered power | System / voltage | PF / efficiency | Current |
|---|
Watts to amps conversion table
These values use electrical input watts, single-phase AC and PF = 1, rounded to two decimals. For steady DC the same arithmetic applies. They are reference calculations, not appliance ratings or circuit approvals.
| Watts | 120 V | 220 V | 230 V | 240 V |
|---|---|---|---|---|
| 60 | 0.50 A | 0.27 A | 0.26 A | 0.25 A |
| 100 | 0.83 A | 0.45 A | 0.43 A | 0.42 A |
| 300 | 2.50 A | 1.36 A | 1.30 A | 1.25 A |
| 400 | 3.33 A | 1.82 A | 1.74 A | 1.67 A |
| 500 | 4.17 A | 2.27 A | 2.17 A | 2.08 A |
| 700 | 5.83 A | 3.18 A | 3.04 A | 2.92 A |
| 1000 | 8.33 A | 4.55 A | 4.35 A | 4.17 A |
| 1200 | 10.00 A | 5.45 A | 5.22 A | 5.00 A |
| 1400 | 11.67 A | 6.36 A | 6.09 A | 5.83 A |
| 1500 | 12.50 A | 6.82 A | 6.52 A | 6.25 A |
| 1550 | 12.92 A | 7.05 A | 6.74 A | 6.46 A |
| 1800 | 15.00 A | 8.18 A | 7.83 A | 7.50 A |
| 2000 | 16.67 A | 9.09 A | 8.70 A | 8.33 A |
| 3000 | 25.00 A | 13.64 A | 13.04 A | 12.50 A |
| 3600 | 30.00 A | 16.36 A | 15.65 A | 15.00 A |
| 4500 | 37.50 A | 20.45 A | 19.57 A | 18.75 A |
| 4800 | 40.00 A | 21.82 A | 20.87 A | 20.00 A |
| 5000 | 41.67 A | 22.73 A | 21.74 A | 20.83 A |
| 7200 | 60.00 A | 32.73 A | 31.30 A | 30.00 A |
| 10000 | 83.33 A | 45.45 A | 43.48 A | 41.67 A |
Watts to amps formulas
| System | Current formula | Input voltage |
|---|---|---|
| Steady DC | I = P / V | Across the load |
| Single-phase AC | I = P / (V × PF) | RMS voltage across the load |
| Balanced three-phase AC | I = P / (√3 × VLL × PF) | RMS line-to-line voltage |
P is total electrical input power in watts, I is current in amperes, and PF is true power factor. For three-phase, P is the total power across the three phases and I is line current. Do not divide total power by three again.
For a single 240 V load connected across the two hot conductors of a split-phase supply, use the single-phase formula with 240 V. If you have separate 120 V loads on the two legs, calculate each leg separately; one total wattage does not determine both line currents or neutral current.
Changing voltage in the calculator keeps entered power fixed. Actual equipment may not maintain the same power when its supply voltage changes. Use the rated supply and operating measurements for your equipment.
What are watts, volts and amperes?
An ampere is a unit of electric current: one coulomb of charge passing a point per second. A watt measures power, or one joule per second. A volt measures electrical potential difference. Watts and amps are different quantities connected through voltage and, in AC, power factor.
For example, 1500 W at 120 V and PF 1 corresponds to 12.5 A. With the same 1500 W input and PF 0.8, the calculated current is 15.625 A. Power factor and motor efficiency describe different relationships and should not be used interchangeably.
Amps to watts: the reverse calculation
DC: P = V × I. Single-phase AC: P = V × I × PF. Balanced three-phase AC: P = √3 × VLL × I × PF. These formulas return electrical input power, not motor shaft output.
| Current | 120 V single-phase | 240 V single-phase | 480 V three-phase |
|---|---|---|---|
| 5 | 600 W | 1,200 W | 4,156.92 W |
| 10 | 1,200 W | 2,400 W | 8,313.84 W |
| 15 | 1,800 W | 3,600 W | 12,470.77 W |
| 20 | 2,400 W | 4,800 W | 16,627.69 W |
| 30 | 3,600 W | 7,200 W | 24,941.53 W |
| 40 | 4,800 W | 9,600 W | 33,255.38 W |
| 50 | 6,000 W | 12,000 W | 41,569.22 W |
Use the amps to watts calculator for custom reverse conversions.
Six worked watts to amps examples
1. A 1500 W load at 120 V
With single-phase electrical input and PF 1: 1500 / 120 = 12.5 A. Whether an existing branch circuit can supply it also depends on the equipment instructions, other loads, operating duration and applicable installation requirements.
2. A 4500 W heating element at 240 V
For the element alone at PF 1: 4500 / 240 = 18.75 A. This calculation does not specify a breaker rating or wire gauge. Additional elements, controls and the complete equipment rating must be considered separately.
3. A 4800 W element at 240 V
4800 / 240 = 20 A at PF 1. If this is one part of an appliance, it is not automatically the current of the complete appliance. Use the complete nameplate data rather than assuming a fixed additional motor current.
4. A 60 W DC load at 12 V
60 / 12 = 5 A at that operating point. If the 12 V output is supplied by an AC adapter, the adapter’s AC input current is a separate calculation using its input voltage, efficiency and power factor.
5. A three-phase motor delivering 1000 W at the shaft
Assume 480 V line-to-line, PF 0.82 and efficiency 0.88. Electrical input is 1000 / 0.88 = 1136.363636 W. Line current is 1136.363636 / (√3 × 480 × 0.82) = 1.666870 A. Select Motor shaft output watts to include efficiency once.
6. A 2000 W AC input at 220 V and PF 0.85
2000 / (220 × 0.85) = 10.695187 A for a single-phase load. Do not apply motor efficiency again when the 2000 W value already represents measured electrical input.
Motor watts: input, shaft output and efficiency
First identify what the stated power describes. Shaft power is mechanical output; measured electrical watts describe input. At an operating point with efficiency η, input W = output W / η. The calculator’s input-power mode does not apply efficiency, while output-power mode divides by the entered efficiency before calculating current.
For a single-phase motor delivering 3730 W with efficiency 0.86 and PF 0.82 at 240 V, current is 3730 / (0.86 × 240 × 0.82) = 22.038665 A. The PF and efficiency here are example assumptions, not defaults for all motors.
Efficiency and power factor vary with operating load. The U.S. Department of Energy explains motor input-power and loading relationships in Determining Electric Motor Load and Efficiency. This calculator estimates running current at the specified operating point; it does not calculate starting current, overload settings or protective-device selection.
For other motor inputs, use HP to amps or the three-phase current calculator.
Quick watts to amps answers
All values below use electrical input power, single-phase voltage across the load, and PF 1. The full table above covers additional voltages.
| Question | Calculated answer |
|---|---|
| 500 watts at 120 volts | 4.166667 A |
| 1000 watts at 120 volts | 8.333333 A |
| 1400 watts at 120 volts | 11.666667 A |
| 1500 watts at 120 volts | 12.500000 A |
| 1800 watts at 120 volts | 15.000000 A |
| 2000 watts at 120 volts | 16.666667 A |
| 3000 watts at 240 volts | 12.500000 A |
| 4500 watts at 240 volts | 18.750000 A |
| 4800 watts at 240 volts | 20.000000 A |
| 5000 watts at 240 volts | 20.833333 A |
| 10000 watts at 240 volts | 41.666667 A |
Frequently asked questions
Can I convert watts to amps without voltage?
No. The same power can correspond to different currents at different voltages. Use the actual load voltage and supply arrangement, not a country-wide assumption.
How many amps is 1500 watts at 120 volts?
12.5 A at PF 1. At PF 0.8 the same electrical input is 15.625 A. The calculated current alone does not approve a particular branch circuit.
How many amps is 4500 watts at 240 volts?
18.75 A for a single-phase load at PF 1. If 4500 W describes mechanical output, also include efficiency to determine electrical input.
Does a three-phase result mean current per phase or total current?
The result is line current for the balanced system. Do not add the three line currents together and call that the equipment current rating.
Can I use this for an unbalanced three-phase load?
The single total-power formula assumes balance. Unbalanced loads require phase-specific voltage, current and power information; this calculator does not determine their neutral current.
Can I use power factor 1 for a motor or power supply?
Only if it is appropriate to that equipment and operating point. Otherwise use measured or manufacturer-specified power factor. For nonlinear loads, true power factor includes distortion effects and may differ from displacement cos φ.
Will the result tell me what breaker or cable to use?
No. Running-current estimation is one input to a separate installation design. Equipment instructions, applicable rules, conductor conditions, continuous loading and starting behavior may also matter.
How do I compare or export results?
Calculate a case and choose Save case. Repeat for up to three cases, then download the CSV. The file records voltage, system, power basis, PF and efficiency so each result retains its assumptions. Nothing is saved after leaving or reloading the page.