Ohm's Law Calculator
Enter any two of volts, amps and ohms, and it works out the third, plus the power in watts.
Ohm's law links voltage, current and resistance in a simple resistive circuit: Volts = Amps × Ohms. Pick what you want to find, then fill in the other two.
1. What do you want to work out?
The box you're working out is greyed out. Fill in the other two.
2. What you know
1 kΩ = 1,000 Ω
3. Results
How it was worked out
What this does and doesn't tell you
- Ohm's law works for resistive loads such as heater elements, filament globes and resistors. Motors, LED drivers, chargers and electronics don't behave like a simple resistor, so use the equipment's rated current for those.
- A resistance reading taken with a multimeter on a cold heater element or globe is lower than its hot, working resistance, so the current worked out from it will be on the high side.
- The power figure is for DC or a resistive AC load. It doesn't allow for power factor.
- 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
New to these numbers? Read Volts, Amps, Watts and Ohms Explained. To measure them, see How to Use a Multimeter Safely. To go from watts to amps, use the Watts, Amps & Volts 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.