Ohm's Law Calculator
Enter any two values to calculate the rest
Formulas Used
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.