Watts, Amps & Volts Calculator
Enter any two of watts, amps and volts, and it works out the third. Works for DC and AC.
Power is volts multiplied by amps: Watts = Volts × Amps. Use it to read an equipment label, or to see how much current a load draws at 12V compared with 240V AC.
1. What do you want to work out?
The box you're working out is greyed out. Fill in the other two.
Only used for AC. Use 1 for heaters and kettles. Motors and some electronics are lower. Check the label or manual.
2. What you know
Common: 5V USB, 12V or 24V DC, 240V AC
3. Results
How it was worked out
What this does and doesn't tell you
- It uses the figures you enter. A label's watts are often a maximum, and motors, fridges and compressors draw more at start-up. Use the maker's figures when sizing cable, fuses and batteries.
- For AC, real power = volts × amps × power factor. If you don't know the power factor, 1 gives the lowest current, so treat the result as a minimum.
- The same watts mean very different currents at different voltages. A 120W load is about 10A at 12V but only about 0.5A at 240V AC. That's why 12V systems need heavier cable.
- 240V AC mains can kill. In Australia, work on household mains wiring must be carried out by a licensed electrician.
- Low-voltage DC systems can still deliver very high current. A short across a battery can cause burns, fire or a battery explosion.
Next steps
Read Volts, Amps, Watts and Ohms Explained and 12V Wiring Basics. For battery capacity, use the mAh, Ah & Wh Converter. For resistance, use the Ohm's Law Calculator.
Technical note: This is general educational information, not a substitute for a design calculation, manufacturer instructions or applicable Australian standards. Everything is worked out in your browser. Nothing is saved or sent anywhere.