Ohm's Law Calculator
Ohm’s law calculator: V = I·R. Find voltage, current or resistance, plus the power dissipated by the resistor.
V = I · R
How to use this calculator
- Choose the quantity you want under “Solve for”.
- Type the known values and pick their units: any combination works.
- The result updates as you type. Open “Show the steps” to see the substitution.
Ohm’s law states that the voltage across a resistor equals the current through it times its resistance, V = I·R.
The calculator also shows the power dissipated, P = V·I, so you can check that a resistor’s power rating is high enough.
Formula
V = I · R
| Symbol | Quantity | Units |
|---|---|---|
| I | Current | A, mA, µA, kA |
| R | Resistance | Ω, mΩ, kΩ, MΩ |
| V | Voltage | V, mV, µV, kV |
Worked example
Given: I = 2 A · R = 5 Ω
V = I · R
Result: V = 10 V
Frequently asked questions
What resistor do I need for an LED?
R = (Vsupply − VLED)/I. With 5 V, a 2 V LED and 20 mA: R = 3/0.02 = 150 Ω.
Does Ohm’s law apply to every component?
Only to ohmic conductors such as resistors and metal wires at constant temperature. Diodes and lamps are non-ohmic.