Ohm's Law Calculator

Calculate voltage, current, resistance, and power from any two known electrical values using Ohm's Law.

Results

Visualization

How It Works

Ohm's Law is the foundation of electrical engineering. It describes the relationship between voltage (V), current (I), and resistance (R) in a circuit. Combined with the power equation, any two known values let you calculate the other two.

The Formula

V = I x R  |  P = V x I  |  P = I² x R  |  P = V² / R

Variables

  • V — Voltage in volts (V) -- the electrical pressure pushing current through the circuit
  • I — Current in amperes (A) -- the flow rate of electrical charge
  • R — Resistance in ohms (ohm) -- opposition to current flow
  • P — Power in watts (W) -- the rate of energy consumption or delivery

Example

A 120V circuit drawing 10A: R = 120/10 = 12 ohms. P = 120 x 10 = 1,200 watts. This is a typical space heater's electrical profile.

Tips

  • Remember the Ohm's Law wheel: write V=IR and P=VI, then solve algebraically for any unknown.
  • Current is the dangerous part of electricity -- as little as 0.1A through the body can be fatal.
  • Doubling the voltage across a fixed resistance quadruples the power (P = V squared / R).
  • Use this calculator to verify circuit measurements with a multimeter.
  • In AC circuits, these formulas apply to RMS (root mean square) values, not peak values.