Ohm's law and power calculator
Fill in any two boxes. The other two are worked out for you, and you can change your mind at any time.
- 1Type your numbersUse the white boxes. Tap an example chip if you want a starting point.
- 2Read the answerThe green panel updates as you type. You cannot edit it.
- 3See whyThe steps below show the formula with your numbers filled in.
Fill in any two boxes. The other two turn green and fill themselves in. Typing in a green box swaps it in.
What this means
Voltage pushes current through a resistance. Ohm's law ties the three together: voltage equals current times resistance.
Power is how much energy the circuit uses each second, measured in watts. It equals voltage times current. Combine the two rules and you can find any quantity from any two of the others.
Write down what the question gives you and what it asks for, then pick the formula that has exactly those. The table below shows every combination.
92 questions in the official pools involve this topic:
Common questions
Which two boxes should I fill in?
Any two. The calculator keeps the two you edited most recently and works out the other two, so you can switch between, for example, voltage and current, or voltage and resistance.
What is the difference between watts and volts?
Volts measure the electrical push. Amps measure how much current flows. Watts measure the work being done, which is volts times amps.
Does this work for AC?
Yes for resistive loads such as a dummy load, using RMS values. Circuits with coils and capacitors need reactance, which is not covered here.