The Circuit Maker

Ohm's Law Calculator

Calculate voltage, current, resistance, or power. Enter any two known values and the calculator will solve for the remaining values using Ohm's Law (V = I × R) and the power equation (P = V × I).

V
A
Ω
W

How to use this calculator

Enter any two of the four values — voltage, current, resistance, or power — and click Calculate. The calculator uses Ohm's Law and the power equation to solve for the unknown values.

Ohm's Law formulas

Ohm's Law describes the relationship between voltage (V), current (I), and resistance (R) in an electrical circuit:

  • V = I × R — Voltage equals current times resistance
  • I = V / R — Current equals voltage divided by resistance
  • R = V / I — Resistance equals voltage divided by current

Power formulas

Electrical power (P) can be calculated using any two of the three Ohm's Law values:

  • P = V × I — Power equals voltage times current
  • P = I² × R — Power equals current squared times resistance
  • P = V² / R — Power equals voltage squared divided by resistance

Example calculation

If you have a 12V power supply and a 220Ω resistor, enter 12 in the Voltage field and 220 in the Resistance field. The calculator will show that the current is approximately 54.5 mA and the power dissipation is about 0.65W.