About the Watts, Amps and Volts Calculator
This calculator converts between watts, amps and volts. Pick the circuit type (DC, AC single-phase or AC three-phase), choose which quantity you want, and type the other two. For AC circuits you also enter the power factor, which is 1 for heaters and often about 0.8 for motors. The answer appears as you type, in a sensible unit, with the formula written in words and the same value in other units. The formulas are the ideal ones for steady operation: they do not include cable losses, starting current or changes in power factor with load, and three-phase results assume a balanced load with line-to-line voltage. It is a quick helper, not a replacement for an electrician's calculation or local wiring rules.
Updated September 2026
How to use the Watts, Amps and Volts Calculator
- 1Choose DC, AC single-phase or AC three-phase.
- 2Choose whether to calculate watts, amps or volts.
- 3Type the two known values and pick their units.
- 4For AC, check the power factor. Use 1 if you are unsure and the load is a heater.
- 5Read the result, the formula and the unit table, or copy the answer.
The three formulas
Power in watts is voltage in volts multiplied by current in amps. Rearranged, amps equal watts divided by volts, and volts equal watts divided by amps. Everything else on this page is a small correction to these three lines.
Because you choose which quantity to calculate, the tool always uses the correct rearrangement and tells you which one it used. It also stops with a plain message if a division by zero would happen, for example when the volts are 0.
DC, single-phase and three-phase
- DC: batteries, solar panels, chargers and car electrics. Power = volts × amps.
- AC single-phase: household sockets. Power = volts × amps × power factor.
- AC three-phase: workshops, pumps and large motors. Power = √3 × line voltage × amps × power factor.
- In three-phase circuits, the voltage entered is the one between two lines, such as 400 V, not the one between a line and neutral.
Power factor explained
In AC circuits the current can lag behind the voltage, and only part of the product of volts and amps becomes useful power. The useful share is the power factor. A heater has a factor of 1, so its watts equal volts times amps. A lightly loaded motor may drop to 0.6 or lower.
If you do not know the factor, 0.8 is a common assumption for motors and 1 for heaters. Enter the real figure from the nameplate whenever you have it, because the current changes noticeably with it.
Worked examples for common appliances
A phone charger delivering 5 V at 2 A uses 10 W. A kettle on a 230 V supply drawing 10 A with a power factor of 1 uses 2,300 W, or 2.3 kW. A three-phase motor at 400 V drawing 10 A with a power factor of 0.8 uses about 5.54 kW.
For the energy those loads use over time, see Electricity Cost Calculator, and for apparent power in kVA use kVA to kW Calculator. Use Ohm's Law Calculator when you know resistance rather than power.
Features
- Watts, amps and volts in one page
- DC, single-phase and three-phase formulas
- Power factor for AC loads
- Units W, kW, mW, A, mA, V, kV and mV
- Formula shown in words
- One-tap examples for common devices
- Runs in your browser, nothing is sent anywhere
Frequently asked questions
How do I convert watts to amps?
Divide the watts by the volts. For a DC circuit that is all you need: 24 W at 12 V is 2 A. For AC, also divide by the power factor, and for three-phase, by 1.732 as well. The calculator does each step once you choose the circuit type.
What is power factor and what value should I use?
Power factor is the share of the current that does real work in an AC circuit, from 0 to 1. Resistive loads such as heaters and kettles are 1. Induction motors are commonly about 0.8, and modern electronic equipment often lies between 0.9 and 0.95. Use the value on the nameplate when there is one.
How do I convert amps to watts for three-phase?
Multiply 1.732 by the line-to-line voltage, the current and the power factor. Ten amps at 400 V with a power factor of 0.8 gives about 5,543 W. Choose AC three-phase and Watts, then type 400 V and 10 A.
What is the difference between DC and AC formulas?
DC power is simply volts times amps. In AC, the voltage and current swing up and down together only partly, so the real power is smaller by the power factor. Three-phase supplies deliver three such currents, which brings in the 1.732 factor.
How many amps is 1000 watts at 230 volts?
About 4.35 amps when the power factor is 1, since 1000 divided by 230 is 4.348. With a power factor of 0.8 the current rises to about 5.43 amps, because more current is needed for the same real power.
Can I use this to size a circuit breaker?
Only as a first estimate. Breakers and cables must also allow for starting current, ambient temperature, cable length, grouping and local regulations. Ask a qualified electrician before choosing protective devices.