Ohm's Law Calculator

Solve any of voltage, current, resistance, or power from the two you know, using Ohm’s law and the power equation. Calculates in your browser.

Enter any two values, the other two are calculated.

Voltage-
Current-
Resistance-
Power-

Show the math

Ohm's law links voltage, current, and resistance; power is voltage times current:

V = I × R  ·  P = V × I

Give any two quantities and the calculator rearranges these to find the rest. All math runs locally in your browser.

What this does

An Ohm's law calculator solves any of voltage, current, resistance, or power from the two you already know, using Ohm's law and the power equation.

How to use it

  1. Enter any two known values.
  2. Leave the unknowns blank.
  3. Read the remaining quantities.
  4. Switch units as needed.

How it works

Ohm's law links voltage, current, and resistance. Power can also be written P = I²R or P = V² ÷ R, so any two known quantities give the rest.

V = I × R; P = V × I

Understanding your result

The four quantities are locked together, so changing one forces the others, which is the real lesson here: drop the resistance at a fixed voltage and current (and heat) climb fast. Use the power figure to size components, because a resistor that is correct on resistance but underrated on wattage will overheat, and treat these as ideal values that ignore wire resistance and temperature drift.

Example

12 V across 4 Ω draws 3 A and dissipates 36 W.

Sources & methodology

Last updated .

Frequently asked questions

What is Ohm’s law?

Ohm’s law states that voltage equals current times resistance: V = I × R. Rearranged, I = V ÷ R and R = V ÷ I.

How is power found?

Power is voltage times current, P = V × I. It can also be written P = I²R or P = V² ÷ R, so any two known quantities give the rest.

Is my data stored?

No. Every calculation runs locally in your browser — nothing is uploaded or saved.