Free Engineering Tool
Cables and circuits
Ohm's Law and Power Calculator
Type any two values. The two you touched last are your inputs, and the other two are worked out for you.
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- Runs in your browser
- Your numbers never leave your device
Inputs
V
A
Ω
W
Tinted fields are calculated. Type in a tinted field to make it an input instead.
Try an example
Readout
I-A
P-W
The formulas
V = I × R · P = V × I · P = I² × R · P = V² / R
These hold for DC and for AC circuits that are purely resistive. For AC loads with inductance or capacitance (motors, transformers), use the power calculator, because power factor then matters.
Where it helps on the bench
- Insulation leakage: a megger applying 500 V that sees 0.5 µA of leakage is reading 1000 MΩ. Enter 500 V and 0.0000005 A to check.
- Heater or lamp check: measure the cold resistance with a multimeter and compare with the rated power. Heating elements read higher when hot.
- Burden and shunt checks: find the power a resistor must dissipate, then pick a part with at least twice that rating.
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