Ohm's Law Calculator

Fill any 2 of 4 quantities — Voltage, Current, Resistance, Power — and the other two solve instantly.

Enter values in any two fields to calculate the remaining two.

V Voltage

I Current

R Resistance

P Power

All 12 Ohm's Law Formulas

Voltage from I, R

V = I × R

Voltage from P, I

V = P / I

Voltage from P, R

V = √(P × R)

Current from V, R

I = V / R

Current from P, V

I = P / V

Current from P, R

I = √(P / R)

Resistance from V, I

R = V / I

Resistance from V, P

R = V² / P

Resistance from P, I

R = P / I²

Power from V, I

P = V × I

Power from V, R

P = V² / R

Power from I, R

P = I² × R

About Ohm's Law

Ohm's Law states that the voltage across a conductor is directly proportional to the current flowing through it, with resistance as the constant of proportionality: V = I × R. It is one of the most fundamental relationships in electrical engineering.

Voltage (V) is measured in volts and represents electrical potential difference. Current (I) is measured in amperes (amps) and is the flow rate of electric charge. Resistance (R) in ohms (Ω) opposes current flow. Power (P) in watts is the rate of energy transfer.

Ohm's Law is used everywhere — from sizing resistors in electronics, calculating wire requirements in home wiring, designing audio amplifiers, to troubleshooting automotive electrical faults.