Solve for voltage, current, resistance or power. Fill in any two of the four values and the calculator gives you the other two using Ohm’s law and the power formulas.
Fill in any two boxes. The other two are calculated. If you fill in more than two, voltage and current are used first, then voltage and resistance, and so on.
Formulas and assumptions
- Ohm’s law: V = I times R
- Power: P = V times I
- Also: P = I squared times R, and P = V squared divided by R
- Units: volts (V), amps (A), ohms (ohm), watts (W)
Example
A heater connected to 230 V that draws 5 A has a resistance of 230 divided by 5, which is 46 ohms, and uses 230 times 5, which is 1150 W.
Frequently asked questions
What is Ohm’s law?
It says the voltage across a conductor equals the current through it times its resistance, written V = I times R.
How do I find power from voltage and current?
Multiply them. A 230 V appliance drawing 5 A uses 1150 W.
Does Ohm’s law work for AC?
Yes, for resistive loads such as heaters and incandescent lamps. For motors and other reactive loads you also need power factor and impedance.
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