Calculate electrical relationships V = I × R and P = V × I for DC circuit analysis.
Overview
Ohm's law states that voltage across a linear resistor equals current times resistance: V = I × R. Knowing any two of voltage (volts), current (amperes), and resistance (ohms) determines the third.
Power dissipation in watts often accompanies Ohm calculations: P = V × I, equivalently I²R or V²/R. These help size resistors, fuses, and wire gauges before building circuits.
Sign conventions matter in circuit analysis: current direction, voltage polarity, and whether components are in series or parallel. This calculator assumes a simple single-resistor relationship for quick estimates.
For AC circuits with reactance, impedance replaces resistance. Use this tool for introductory DC breadboard work, battery loads, and electronics homework—not for complex AC power-factor designs without additional models.
Steps
Provide any two of V, I, R as available.
Select the value to solve.
Apply Ohm's law rearrangement.
Derive watts from V and I if shown.
Use volts, amperes, and ohms consistently.
Compare power with component ratings.
Math
V = I × R; P = V × I
Voltage drives current through resistance. Power is the rate of energy transfer in the load.
Worked cases
I = V/R = 24/8
3 A.
V = 2×15
30 V.
P = 12×1.5
18 W.
Why use this
Questions