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Ohm’s Law Calculator: Voltage, Current, Resistance & Power
Find V, A, Ω and W from two known values. Results include the values and assumptions used.
Formula and worked example
V = I × R
P = V × I = I² × R = V² / R
P = V × I = I² × R = V² / R
How to use the calculation
Choose the two quantities you know, then their units. Results use base units: volts, amperes, ohms and watts. The tool works with non-negative magnitudes and positive resistance. Pairs without a known resistance require non-zero values to keep the solution finite and unique.
Worked example
A 12 V DC supply and 2 A current correspond to 6 Ω resistance and 24 W power. Equivalently, choosing 6 Ω and 24 W produces 12 V and 2 A.
Common questions
Can I enter milliamps or kilo-ohms?
Yes. Select mA or µA for current, kΩ or MΩ for resistance, and the available voltage/power units. The result is converted back to base units.
Does this fully solve a motor or capacitor AC circuit?
No. Reactive AC circuits require impedance and phase-angle information. Use the motor or power-factor tool for their stated applications.
Can voltage or power be zero?
With a known positive resistance, a zero voltage, current or power can have a unique zero-output solution. A zero in a pair without known resistance can be ambiguous or require infinite resistance, so that case is not calculated.
Related electrical guides
More electrical calculators
Motor CurrentConvert motor kW or HP to running current.kVA ↔ AmpsConvert kVA to amps, or amps back to kVA.Electricity CostEstimate energy units and cost for multiple loads.Voltage DropCheck voltage drop using copper or datasheet R/X.Power Factor / kVAREstimate kvar needed to improve lagging power factor.
Formula references
Formula review: 31 October 2026. Examples are illustrative; use your actual equipment and project data.
