dopecalc

Ohm's Law Calculator

Calculate voltage, current, resistance, or power using Ohm's law (V = IR) and the power equation (P = VI).

Enter any two of voltage, current, or resistance. The calculator solves for the third using Ohm's law (V = IR) and computes power (P = VI).

V
A
Ω

Ohm's Law Triangle

V
───
I × R
V = I × R
I = V / R
R = V / I

About this Calculator

Calculate voltage, current, resistance, or power using Ohm's law (V = IR) and the power equation (P = VI).

Formula & Calculations

Formula

V = I × R, I = V / R, R = V / I, and P = V × I
Where:
  • V=Voltage — electrical potential difference (Volts)
  • I=Current — flow of electric charge (Amperes)
  • R=Resistance — opposition to current flow (Ohms)
  • P=Power — rate of energy transfer (Watts)

Assumptions

  • The circuit follows Ohm's law (linear relationship between V and I).
  • Power is calculated as the product of voltage and current.
  • Provide any two of V, I, and R to solve for the third. Power is always calculated.

Calculation Examples

Example 1

Inputs:Voltage = 12 V, Resistance = 4 Ω
Result:Current = 3 A, Power = 36 W

I = 12 / 4 = 3 A, P = 12 × 3 = 36 W.

Example 2

Inputs:Current = 2 A, Resistance = 10 Ω
Result:Voltage = 20 V, Power = 40 W

V = 2 × 10 = 20 V, P = 20 × 2 = 40 W.

Example 3

Inputs:Voltage = 230 V, Current = 5 A
Result:Resistance = 46 Ω, Power = 1150 W

R = 230 / 5 = 46 Ω, P = 230 × 5 = 1150 W.

Frequently Asked Questions

What is Ohm's law?

Ohm's law states that the current through a conductor is directly proportional to the voltage across it and inversely proportional to the resistance: V = IR. It is fundamental to electrical circuit analysis.

How do I know which two values to enter?

Enter any two of voltage (V), current (I), and resistance (R), and the calculator will solve for the missing one. Power (P) is always calculated from the known values.