⚡ Ohm's Law Calculator
Ohm's law (V = I × R) ties voltage, current and resistance together: know any two and the third is fixed. Pick what to solve for, enter the other two, and get the answer plus the power involved.
The power figure matters for part selection — a resistor must be rated above the watts it will actually dissipate.
How to use this calculator
Choose whether to solve for voltage, current or resistance, enter the other two values, and get the answer plus the power dissipated.
- Pick what to solve for in the Solve for menu.
- Enter the two known values; leave the unknown at zero.
- The result appears instantly with no button to press.
- Check the power figure when choosing component ratings.
Frequently asked questions
What is Ohm's law?
Voltage equals current times resistance (V = I x R). Knowing any two of the three values fixes the third, which is what this calculator solves.
Can you give a worked example?
2 amps through 6 ohms gives 12 volts. 12 volts across 6 ohms gives 2 amps. 12 volts at 2 amps means 6 ohms of resistance. Each case dissipates 24 watts.
Why does it also show power?
Power tells you how much heat a component must handle. A resistor must be rated above the watts it will actually dissipate, or it will overheat.
What units does it use?
Volts, amps and ohms, the standard SI electrical units, with power in watts.