Ohm's Law Calculator: Volts, Amps, Ohms & Watts

🔗 Open the full-page Ohm’s Law Calculator

The relationships

For many practical problems, V = I × R and P = V × I are enough to reason about circuits. Equivalent forms P = I²R and P = V²/R explain why heat rises quickly when current increases.

How to use this tool

Enter any two of:

• Voltage (volts)
• Current (amps)
• Resistance (ohms)
• Power (watts)

The calculator fills in the rest. Values must be positive numbers suitable for the physical scenario you are modeling.

AC note

For sinusoidal AC into resistive loads, RMS volts and amps behave like DC in these formulas. Reactive loads (motors, many LED drivers) need more advanced analysis.