eGigFree Ohm’s Law Calculator: Volts, Amps, Ohms and Watts
Enter any two of voltage, current, resistance and power to work out the other two.
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Ohm’s law formulas
Voltage: V = I × R. Current: I = V ÷ R. Resistance: R = V ÷ I.
Power: P = V × I = I² × R = V² ÷ R.
Example: a 1,000 W heater on 230 V draws I = 1000 ÷ 230 = 4.35 A, and has a resistance of R = 230² ÷ 1000 = 52.9 ohms.
These hold for resistive loads such as heaters. Motors and other AC loads also have a power factor, so the current can be higher than this shows.
Questions people ask
What is Ohm’s law?
Voltage equals current times resistance: V = I × R. If you know any two, you can work out the third.
How do I work out amps from watts?
Amps = watts ÷ volts for a simple resistive load. A 2,000 W geyser on 230 V draws about 8.7 A. Motors and other AC loads draw more, because of their power factor.
Does Ohm’s law apply to everything?
It holds well for resistors and heating elements. LEDs, motors and other electronic parts do not follow it in a simple way.
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