What this calculator does
Find out how many amps a device draws from its watts, or how many watts from its amps. Watts (W) measure how much power a device uses. Amps (A) measure how much electric current flows through the wires to deliver it. Voltage (V), the push behind the current, links the two. At the same voltage, more watts always means more amps. That's why a 1,500 W space heater on a 120 V outlet draws 12.5 A, while a 60 W lamp draws only half an amp.
The converter works both ways, and it can also find the voltage when you know the other two. It handles the three kinds of power you'll meet. DC (direct current) comes from batteries and solar systems. Single-phase AC (alternating current) is the ordinary power in homes. Three-phase AC is used in commercial buildings and workshops. For AC, it includes the power factor, which matters for motors and many electronics. Below the answer, a chart lists the amps for common wattages at your voltage. That makes it easy to compare several appliances at a glance.
Where it's used
Why this math matters outside the classroom:
- Kitchen circuits. A cook checks that a 1,200 W microwave and a 1,500 W kettle on one 120 V circuit draw 10 A + 12.5 A, too much for 20 A.
- Camping power. A camper finds that a 60 W fridge on a 12 V battery draws 5 A, so a 100 Ah battery runs it about 20 hours.
- Workshop motors. A shop owner works out that a 10 kW three-phase machine at 480 V and power factor 1 draws about 12 A per line.
- EV charging. An electrician notes a 7,200 W home charger on 240 V draws 30 A, so it needs a 40 A circuit under the 80% rule.
- Science class. Students use P = V × I to show a 6 V motor drawing 0.5 A uses 3 W.
Grade level and standards: Grades 6–7; Common Core State Standards for Mathematics 6.EE.A.2.c. © Copyright 2010. National Governors Association Center for Best Practices and Council of Chief State School Officers. All rights reserved.
How to use it
- Choose the supply: DC, AC single-phase (household outlets and most appliances) or AC three-phase.
- Choose what to convert: watts to amps, amps to watts, or volts from watts and amps.
- Enter the numbers you know. For three-phase, use the line-to-line voltage (measured between two of the three power wires), such as 208, 400 or 480 V.
- For AC, enter the power factor. Use 1 for heaters and old-style bulbs, or the number on the motor's label. Read the answer, then check the chart for other wattages.
What the inputs mean
- Power
- The power the device actually uses, in watts. Appliance labels usually show it. For kilowatts (kW), multiply by 1,000.
- Current
- For three-phase, the current in each of the three power wires.
- Voltage
- Home circuits in North America are 120 V or 240 V. Much of the world uses 230 V. Three-phase supplies are measured line to line, between two of the power wires.
- Power factor
- The share of the current that does useful work. It's 1 for simple heating loads like heaters and kettles. Motors often run between 0.8 and 0.9. If a label gives only VA or kVA (volt-amps), that number already includes the power factor.
Formula and method
DC: I = P ÷ V AC single-phase: I = P ÷ (V × PF) AC three-phase: I = P ÷ (√3 × V(L-L) × PF) Amps to watts: P = V × I (DC), P = V × I × PF (1-phase), P = √3 × V × I × PF (3-phase) Apparent power: S = P ÷ PF
In the formulas, I is the current in amps, P is the power in watts and V is the voltage. PF is the power factor, and V(L-L) is the line-to-line voltage. S is the apparent power, in volt-amps (VA). √3 is the square root of 3, about 1.732.
Power is voltage times current. In a DC circuit, that's the whole story, so amps are watts divided by volts.
In an AC circuit with motors or electronics, the current and voltage get slightly out of step. So some of the current flows without doing useful work. The power factor, a number from 0 to 1, measures this. The useful power is V × I × PF. A lower power factor means more amps for the same watts.
A balanced three-phase supply delivers power on three wires at once. Using the line-to-line voltage, the total power is √3 times V × I × PF. So each wire carries less current than a single-phase circuit at the same voltage would. The apparent power S is what cables, breakers and transformers really have to carry.
Worked example
How many amps does a 1,500 W space heater draw on a 120 V household circuit?
- A heater turns electricity straight into heat (a resistive load), so the power factor is 1.
- Single-phase AC: I = P ÷ (V × PF).
- I = 1,500 ÷ (120 × 1) = 12.5 A.
Result: The heater draws 12.5 A. That fits on a 15 A circuit, but leaves little room for anything else.
Understanding the result
The amps tell you whether a circuit can handle a device. A common US rule of thumb is to keep loads that run for hours to about 80% of the breaker rating. That's 12 A on a 15 A circuit, or 16 A on a 20 A circuit. Local electrical codes set the actual rules.
Doubling the voltage halves the current for the same power. That's why big appliances like ovens, dryers and EV chargers use 240 V circuits.
Assumptions and limitations
- The device is running steadily. Motors and compressors draw several times their running current for a moment when they start.
- Three-phase loads are balanced, with the same current in each wire.
- Wattages on labels are maximums or typical values. What a device really draws changes with its settings and how hard it's working.
- This is an estimate for planning. It doesn't replace an electrician sizing wires and breakers to your local electrical code.
- For kVA inputs, reactive power and other related power values, use the electrical power calculator.
Frequently asked questions
How many amps is 1,000 watts?
It depends on the voltage. At 120 V it's about 8.33 A, and at 240 V it's about 4.17 A. At 12 V DC it's about 83.3 A. The chart under the answer lists common wattages at whatever voltage you enter.
How many watts can a 15 amp circuit handle?
At 120 V, 15 A × 120 V = 1,800 W. A common practice is to keep loads that run for hours to 80% of that, which gives 1,440 W. Choose amps to watts and enter 15 A and 120 V to see it.
Why do I need the power factor?
For AC devices with motors or electronic power supplies, the current is higher than watts ÷ volts suggests. Dividing by the power factor accounts for this. Leaving it at 1 would make the current look lower than it really is for those devices.
Which voltage do I use for three-phase?
Use the line-to-line voltage, measured between any two of the three power wires. It's commonly 208 V or 480 V in North America, and 400 V in much of the world. The √3 in the formula already accounts for the three phases.
How this calculator is checked
Method: P = V × I for DC; P = V × I × PF for single-phase AC; P = √3 × V(L-L) × I × PF for balanced three-phase AC (standard electrical engineering relations). The calculation is covered by automated tests with known reference values and edge cases. Last updated 2026-10-18. Found a problem? Tell us.
Embed this calculator
Put this Watts to Amps Converter on your own website or blog for free. Paste this code where you want it to appear: