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Ohm’s Law Calculator

Solve for voltage, current, or resistance with Ohm’s law V = I × R, plus power dissipation.

Voltage
20 V
V = I × R = 2 A × 10 Ω
Power
40 W
Current
2 A
Resistance
10 Ω

Results are for ideal DC circuits. Real-world values vary with temperature, component tolerances, and AC effects. Verify against a qualified engineer before use in safety-critical applications.

How it works

  1. 1Choose what to solve for — voltage, current, or resistance.
  2. 2Enter the two known values in volts (V), amperes (A), or ohms (Ω).
  3. 3The calculator returns the third quantity plus power P = V × I.

Use cases

  • Designing resistor and LED circuits with the correct current-limiting resistance.
  • Troubleshooting faults by cross-checking measured voltage and current.
  • Estimating power dissipation to keep components within their ratings.

Frequently asked questions

What is Ohm’s law?

Ohm’s law states that voltage equals current times resistance: V = I × R. It holds for ideal resistors and most DC circuits at a fixed temperature.

How is power calculated?

Power dissipated is P = V × I. Substituting Ohm’s law gives the equivalent forms P = I² × R and P = V² ÷ R.

What is the V/I/R triangle?

A memory aid: cover the unknown to see the formula — V = I × R, I = V ÷ R, R = V ÷ I. A 12 V supply across 6 Ω gives 2 A and 24 W.

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