Watts to Amps Calculator
Convert watts to amps (W to A) for DC, single-phase and three-phase power
Amps = watts ÷ volts. For example, 1,200 W at 120 V = 10 A. For AC loads divide by volts × power factor, and for three-phase divide by √3 × volts × power factor.
Watts to amps calculator
LiveThree-phase uses line-to-line voltage. For wiring decisions, follow local electrical code.
How to convert watts to amps
Watts measure power, the rate at which energy is used, while amps measure current, the flow of charge through the wire. Voltage is the push that drives that current, so the three are tied together by the power formula P = V × I. Rearranged for current, it becomes I = P ÷ V: for a fixed power, a higher voltage means fewer amps. That is why a 1,200 W appliance draws 10 A on a 120 V outlet but only about 5 A on a 240 V circuit. Starting from a current instead? The amps to watts calculator runs the formula the other way, and the other electrical calculators cover volts, ohms and kVA.
Step by step
- Choose the supply type: DC (batteries, solar, vehicles), AC single-phase (household outlets) or AC three-phase (commercial and industrial).
- Enter the power in watts from the appliance nameplate and the supply voltage.
- For AC, enter the power factor. Use 1 for resistive loads such as heaters and kettles; motors and many electronics are lower, often 0.8 to 0.95.
- Divide the watts by volts × power factor, and by √3 (about 1.732) as well for three-phase.
Worked examples
- Space heater, 120 V: 1,500 W ÷ 120 V = 12.5 A. The same heater on 240 V draws 1,500 ÷ 240 = 6.25 A.
- Motor load, single-phase: a 1,800 W tool at 120 V with a power factor of 0.8 draws 1,800 ÷ (0.8 × 120) = 18.75 A, not the 15 A you would get by ignoring the power factor.
- Three-phase equipment: 10,000 W at 208 V with a power factor of 0.9 draws 10,000 ÷ (1.732 × 0.9 × 208) = 30.84 A per line.
- 12 V DC inverter: 1,000 W ÷ 12 V = 83.33 A from the battery, before inverter losses.
If a nameplate gives horsepower instead of watts, convert it with the hp to kW converter and multiply by 1,000, remembering that a motor's hp is shaft output, so its electrical input is higher.
The power triangle
- P = V × I
- I = P ÷ V
- V = P ÷ I
- Three-phase: P = √3 × V × I × PF
What size breaker do I need for 5,000 watts?
On 240 V, 5,000 W draws 20.83 A, which calls for a 25 A breaker, or a 30 A breaker if the load runs three hours or more, because continuous loads are sized at 125% (26.04 A).
- Find the current with I = P ÷ V, dividing by the power factor too for motor loads.
- If the load is continuous, multiply by 1.25, as NEC 210.20(A) requires.
- Round up to the next standard breaker size from the list in NEC 240.6(A): 15, 20, 25, 30, 35, 40, 45, 50 and 60 A are the common steps.
- Use wire rated for that breaker, and check the appliance instructions, which may name a maximum breaker size.
| Load at 240 V | Current | Smallest standard breaker | Continuous × 1.25 | Smallest breaker if continuous |
|---|---|---|---|---|
| 3,000 W | 12.5 A | 15 A | 15.63 A | 20 A |
| 3,600 W | 15 A | 15 A | 18.75 A | 20 A |
| 4,500 W | 18.75 A | 20 A | 23.44 A | 25 A |
| 5,000 W | 20.83 A | 25 A | 26.04 A | 30 A |
| 7,200 W | 30 A | 30 A | 37.5 A | 40 A |
| 9,600 W | 40 A | 40 A | 50 A | 50 A |
On a 120 V supply the same 5,000 W would draw 41.67 A, far beyond an ordinary branch circuit, which is why loads this large are built for 240 V. The appliance's installation instructions and your local electrical code take priority over this arithmetic, and a licensed electrician should size and install the circuit.
Why does a higher voltage mean fewer amps?
Because power is volts times amps, so for the same watts, doubling the voltage halves the current: a 4,800 W load draws 40 A at 120 V but only 20 A at 240 V.
| Supply | Current for 2,400 W |
|---|---|
| 12 V | 200 A |
| 24 V | 100 A |
| 120 V | 20 A |
| 230 V | 10.43 A |
| 240 V | 10 A |
| 480 V | 5 A |
Lower current is the whole point of higher voltage. The heat lost in a wire is I² × R, so halving the current cuts that loss to a quarter: through 0.2 Ω of wiring, 20 A wastes 80 W, while 10 A wastes 20 W. That is why North American homes put ranges, dryers and water heaters on 240 V, why most countries use 230 V for everything, and why transmission lines run at hundreds of kilovolts.
None of this makes higher voltage safer to touch, and an appliance must only be connected to the voltage on its nameplate. A 120 V heater plugged into 240 V would not draw half the current; its fixed resistance would draw twice the current and four times the power.
Watts to amps chart
Calculated with a power factor of 1 (resistive loads such as heaters and incandescent bulbs). Motors and electronics with a lower power factor draw more current for the same watts.
| Power | 12 V DC | 120 V AC | 230 V AC | 240 V AC |
|---|---|---|---|---|
| 60 W | 5.00 A | 0.50 A | 0.26 A | 0.25 A |
| 100 W | 8.33 A | 0.83 A | 0.43 A | 0.42 A |
| 500 W | 41.67 A | 4.17 A | 2.17 A | 2.08 A |
| 1,000 W | 83.33 A | 8.33 A | 4.35 A | 4.17 A |
| 1,200 W | 100.00 A | 10.00 A | 5.22 A | 5.00 A |
| 1,500 W | 125.00 A | 12.50 A | 6.52 A | 6.25 A |
| 1,800 W | 150.00 A | 15.00 A | 7.83 A | 7.50 A |
| 2,000 W | 166.67 A | 16.67 A | 8.70 A | 8.33 A |
| 3,000 W | 250.00 A | 25.00 A | 13.04 A | 12.50 A |
| 5,000 W | 416.67 A | 41.67 A | 21.74 A | 20.83 A |
Watts vs amps: what is the difference?
Watts and amps are linked by voltage but answer different questions: how much work a load does, and how much current the wiring has to carry.
| Attribute | Watts | Amps |
|---|---|---|
| Quantity | Power (P): the rate energy is used | Current (I): the rate electric charge flows |
| SI definition | 1 W = 1 J/s | 1 A = 1 C/s, fixed since 2019 through the elementary charge |
| Measured with | A plug-in power meter; the utility meter adds it up as kWh | A clamp meter around one conductor, or a multimeter in series |
| Same 1,200 W job on 120 V vs 240 V equipment | 1,200 W either way | 10 A vs 5 A |
| What it sizes | Running cost and energy use | Breakers, fuses and wire gauge |
| On a nameplate | Rated input power, such as 1,500 W | Rated current at the stated voltage, such as 12.5 A at 120 V |
4 key differences
- Watts tell you what a load costs to run; amps tell you whether a circuit can carry it.
- On a 120 V supply each ampere carries 120 W, and on 230 V each ampere carries 230 W, so the same appliance draws roughly half the current in 230 V countries.
- Below unity power factor the amps exceed watts ÷ volts: 2,000 W at 230 V and a power factor of 0.85 draws 10.23 A, not 8.7 A.
- Breakers and cables are rated in amps because conductor heating depends on current (I² × R), not on the watts the load turns into work.
How does power factor change the amps?
A lower power factor raises the current for the same watts: a 1,000 W load on 120 V draws 8.33 A at a power factor of 1 but 10.42 A at 0.8. Current drawn by a 1,000 W load at different power factors, using I = P ÷ (PF × V). The lower the power factor, the more current the circuit carries for the same real power, which is why motors and some power supplies need more circuit capacity than their wattage suggests.
| Power factor | At 120 V | At 230 V | At 240 V |
|---|---|---|---|
| 1 | 8.33 A | 4.35 A | 4.17 A |
| 0.95 | 8.77 A | 4.58 A | 4.39 A |
| 0.9 | 9.26 A | 4.83 A | 4.63 A |
| 0.85 | 9.80 A | 5.12 A | 4.90 A |
| 0.8 | 10.42 A | 5.43 A | 5.21 A |
| 0.7 | 11.90 A | 6.21 A | 5.95 A |
| 0.6 | 13.89 A | 7.25 A | 6.94 A |
Watts to amps for 12 V, 24 V and 48 V DC systems
Battery current for RV, marine, off-grid solar and vehicle loads, from I = P ÷ V. These are ideal values: an inverter feeding AC appliances loses some power, so the battery supplies more. At 90% efficiency, divide the result by 0.9. High DC currents need heavy cable and correct fusing, so size them from the manufacturer's instructions.
| Load | 12 V DC | 24 V DC | 48 V DC |
|---|---|---|---|
| 50 W | 4.17 A | 2.08 A | 1.04 A |
| 100 W | 8.33 A | 4.17 A | 2.08 A |
| 300 W | 25.00 A | 12.50 A | 6.25 A |
| 600 W | 50.00 A | 25.00 A | 12.50 A |
| 1,000 W | 83.33 A | 41.67 A | 20.83 A |
| 1,500 W | 125.00 A | 62.50 A | 31.25 A |
| 2,000 W | 166.67 A | 83.33 A | 41.67 A |
| 3,000 W | 250.00 A | 125.00 A | 62.50 A |
Three-phase watts to amps
Line current for balanced three-phase loads with a power factor of 0.9, from I = P ÷ (√3 × PF × V). 208 V is common in North American commercial buildings, 400 V in Europe and much of the world, and 480 V in US industrial sites. Enter your own power factor in the calculator for other loads. For kilowatt and horsepower ratings, the kW to hp converter helps with motor nameplates.
| Power | 208 V | 400 V | 480 V |
|---|---|---|---|
| 5 kW | 15.42 A | 8.02 A | 6.68 A |
| 10 kW | 30.84 A | 16.04 A | 13.36 A |
| 15 kW | 46.26 A | 24.06 A | 20.05 A |
| 25 kW | 77.10 A | 40.09 A | 33.41 A |
| 50 kW | 154.21 A | 80.19 A | 66.82 A |
| 100 kW | 308.41 A | 160.38 A | 133.65 A |
Why can the amps be higher than watts divided by volts?
Because many AC loads have a power factor below 1: part of the current they draw does no useful work, so the wire carries more amps than watts ÷ volts suggests, even though the watts on the label are correct.
For DC circuits and purely resistive AC loads, watts equal volts × amps and the conversion is exact; a heater element that draws 12.5 A at 120 V has a resistance of 120 ÷ 12.5 = 9.6 Ω, which you can confirm with the Ohm's law calculator. Many AC loads, however, shift the current out of step with the voltage. Motors, compressors, fluorescent ballasts and some switch-mode power supplies all draw current that does not turn fully into useful work. The product of volts and amps then gives apparent power in volt-amperes (VA), while the watts on the label are real power. Power factor is the ratio between them: PF = W ÷ VA.
For sizing wire and breakers, it is the current that matters, so a low power factor needs more capacity. If a label lists both watts and amps, trust the amps figure for circuit planning. Motors also draw an inrush current at start-up that can be several times the running current for a fraction of a second, which is why breakers for motor circuits are chosen differently. To convert watts into kilowatts for energy bills, see the watts to kW converter.
Common watts to amps mistakes
- Using the wrong voltage. North American outlets are nominally 120 V, while large appliances use 240 V. Most of Europe, the UK, India and Australia use 230 V. A 2,000 W kettle draws 16.67 A at 120 V but 8.70 A at 230 V.
- Forgetting √3 on three-phase. Dividing three-phase watts by the line voltage alone overstates the current by about 73%.
- Mixing phase and line voltage. The three-phase formula here uses line-to-line voltage, such as 208 V or 480 V, not the 120 V or 277 V line-to-neutral value.
- Treating peak watts as running watts. Generators and inverters list a surge rating and a continuous rating. Size circuits on the continuous current.
- Filling a circuit to 100%. Loads that run for three hours or more are generally limited to 80% of the breaker rating under the US National Electrical Code, so a 15 A circuit supports 12 A of continuous load.
Safety note: these results are estimates for planning and learning. Wiring, breaker and cable sizing must follow your local electrical code, such as the NEC in the US or the IEC-based rules in your country, and installation work should be done by a licensed electrician.
Sources and further reading
The standards and references behind the numbers on this page. Links open in a new tab.
Standards and official sources
Further reading
- Electric powerWikipedia
Watts to amps FAQs
Short, exact answers to what people ask most.
How many amps is 1,500 watts at 120 volts?
1,500 W ÷ 120 V = 12.5 A. At 240 V the same load draws 6.25 A, and at 230 V about 6.52 A.
How many amps does a 1,000 watt load draw?
At 120 V a 1,000 W resistive load draws 8.33 A, at 230 V it draws 4.35 A and at 12 V DC it draws 83.33 A.
How do I convert watts to amps for three-phase power?
Divide the watts by √3 × power factor × line-to-line voltage. For example, 10,000 W at 208 V and a power factor of 0.9 draws about 30.84 A per line.
Can a 15 amp circuit handle 1,500 watts?
A 1,500 W load at 120 V draws 12.5 A, which is within a 15 A breaker's rating but above the 12 A usually recommended for continuous loads. Avoid running other appliances on the same circuit at the same time.
Why do I need the power factor to convert watts to amps?
On AC, watts measure real power, but the wire carries the full current, which is higher when the power factor is below 1. Dividing by volts × power factor gives the actual current.
How many amps does a 1,000 watt inverter draw from a 12 V battery?
At full load it draws 1,000 ÷ 12 = 83.33 A before losses. With an inverter efficiency of about 90%, the battery supplies roughly 92.6 A.
How many amps is 2,000 watts?
At 120 V, 2,000 W draws 16.67 A; at 230 V it draws 8.7 A and at 240 V 8.33 A.
How many amps is 3,000 watts at 240 volts?
3,000 W ÷ 240 V = 12.5 A at a power factor of 1.
How many amps is 100 watts at 12 volts?
100 W ÷ 12 V = 8.33 A of DC current, before any inverter or converter losses.
How many amps does a 60 watt bulb draw at 120 volts?
A 60 W load at 120 V draws 0.5 A.
How many amps is 10 kW at 240 volts single-phase?
10,000 W ÷ 240 V = 41.67 A at a power factor of 1, or more if the power factor is lower.
Related conversions
Formulas follow the SI definitions of the watt, volt and ampere (BIPM SI Brochure, 9th ed.); continuous-load sizing, the 125% rule and standard breaker ratings are from the US National Electrical Code (NFPA 70), sections 210.20(A) and 240.6(A). Last updated . How we verify our numbers.