Ohm's Law Calculator

Enter any two values to calculate the rest

V
I
Ω
P

Formulas Used

V = I × R

What is Ohm's Law?

Ohm's Law is the fundamental relationship between voltage, current, and resistance in an electrical circuit. It states that the current through a conductor between two points is directly proportional to the voltage across the two points, and inversely proportional to the resistance between them.

V = I × R — Voltage (in volts) equals Current (in amps) times Resistance (in ohms)

Power can be calculated using P = V × I, which combined with Ohm's Law gives us P = I²R and P = V²/R.

Practical Examples

LED Circuit: If you have a 5V supply and want to run an LED that needs 20mA with a 2V forward voltage, you need: R = (5V - 2V) / 0.020A = 150Ω

Power Dissipation: That 150Ω resistor will dissipate P = I²R = (0.020)² × 150 = 0.06W (60mW). A standard ¼W resistor will work fine.