Ohm's Law Calculator
Calculate voltage, current or resistance using Ohm's law. Fill in two of the three fields and leave the third at 0, and the calculator works out the rest.
How to use the Ohm's law calculator
- Enter the two values you know: voltage, current or resistance.
- Leave the field you don't know at 0 — the calculator automatically works it out.
- If you fill in all three fields, the calculator instead checks whether they actually agree.
Ohm's law
Worked example: a component has 12 V across it and 2 A flowing through it. The resistance is 12 ÷ 2 = 6 Ω. If instead you know the resistance and the voltage, find the current with I = V ÷ R, so 12 ÷ 6 = 2 A.
Ohm's law states that the voltage (V) across a conductor equals the current (I) through it multiplied by its resistance (R). Voltage is measured in volts (V), current in amperes (A), and resistance in ohms (Ω).
If you know two of the three values, you can solve the equation for the third: R = V ÷ I to find resistance, or I = V ÷ R to find current.
Frequently asked questions
What is Ohm's law?
Ohm's law describes the relationship between voltage, current and resistance in an electrical circuit: the voltage across a conductor equals the current through it multiplied by its resistance (V = I × R). The law is one of the cornerstones of electrical engineering.
What is the unit for resistance?
Resistance is measured in ohms (Ω), named after Georg Simon Ohm. One ohm is defined as the resistance that produces a current of one ampere when the voltage across the conductor is one volt.
How do I use Ohm's law to calculate power consumption?
Ohm's law gives you voltage, current and resistance, but to find power (and therefore energy consumption) you also need P = U × I. See a power calculator to work out watts and kilowatt-hours from voltage and current.