» Ohm's Law


Ohm's Law: Ohm's law formulas. V=I×R, I=V/R, R=V/I, P=V×I.

Use this Ohm's law calculator to solve voltage, current, resistance, and power in one place for circuit design, troubleshooting, and quick electrical checks.

Ohm's law formulas

$$V = I \times R$$ $$P = V \times I$$

SI units for Ohm's law

Variable Symbol SI Unit
Voltage V volt (V)
Electric current I ampere (A)
Electrical resistance R ohm (Ω)
Power P watts (W)

Initial Data (2/4)

Ohm's Law Calculator FAQ

What is Ohm's law?
Ohm's law describes the relationship between voltage, current, and resistance in a circuit: V = I × R. In this calculator, you can also solve power using P = V × I.

How do I use the 2-of-4 mode?
Select exactly two values to calculate (locked), then enter the other two known values. The calculator will solve the selected outputs dynamically with the matching formulas.

Which formulas are used for power?
Depending on your selected variables, the calculator uses equivalent power formulas such as P = V × I, P = I² × R, or P = V² / R. You can play around with the checkboxes to switch known/unknown values and see which formula is applied.

Can I change units for current, voltage, resistance, and power?
Yes. Each variable has its own unit selector. Values are converted internally to SI base units and converted back to the selected output units.

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