How to Use Ohm's Law

Ohm's law states V = IR. Know any two values and you can find the third. This is the foundation of DC circuit analysis.

Step-by-step

1. Identify known values: voltage (V), current (I), or resistance (R).
2. Select the unknown variable and rearrange: V = IR, I = V/R, R = V/I.
3. Ensure consistent units: volts, amperes, ohms.
4. For power, use P = VI = I²R = V²/R after finding the missing value.
5. Check reasonableness: household circuits are 120/240 V; USB is 5 V.
6. Use our Ohm's Law Calculator to solve any variable instantly.

Open the Ohm's Law Calculator to apply these steps with your own numbers instantly.

Frequently asked questions