SolveTap

SolveTap · Learn the method

Ohm’s Law Calculator

Find voltage, current or resistance from two known quantities using V = IR and show the rearrangement.

Calculate

Enter exactly two quantities. Leave the unknown blank. Use volts, amperes and ohms; resistance must be positive.

Calculations run in your browser. Numeric inputs are not included in analytics events.

Formula and variables

V = IR; I = V/R; R = V/I

V is voltage across the resistor; I is current entering its positive-labelled terminal; R is resistance. Convert milliamps to amps before entering current.

Worked example

A 6 Ω resistor has 12 V across it. I = V/R = 12/6 = 2 A. Check by multiplying: 2 A × 6 Ω = 12 V.

When to use this formula

Use Ohm’s law for an ohmic component under conditions where its resistance is treated as constant. A multi-component circuit may first require equivalent resistance and Kirchhoff’s laws.

Common mistakes

A voltage of zero and current of zero do not determine resistance. Negative voltage and current may be consistent with the chosen direction, but negative resistance is outside this passive-resistor tool.

Can this calculate a diode or an entire circuit?

No. Diodes are generally nonlinear, and a circuit may need several equations. This calculator represents one ohmic relationship.

Related calculators and resources

Learn the method