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Ohm's Law Calculator

Enter any two of voltage, current, and resistance to solve the third. If you enter all three, the calculator checks whether they remain consistent with Ohm's Law.

Inputs

Enter your values

Use the voltage across the same component or resistive path you are analysing.

Enter the current through the component or circuit path you want to check.

Use the resistance for the same load or component as the voltage and current values.

Keep learning

Use the calculator, then keep the full method close.

This topic also has a deeper guide and a printable reference pack, so you can move from the live answer into the method, assumptions, and worked examples without leaving the topic cluster.

Browse Electrical & Electronics guides

Related guides

Electrical & ElectronicsFlagship guide

Ohm's Law and Core Circuit Relationships

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Students, technicians, makers, and engineers who need the core electrical relationships to stay physically meaningful when the circuit is on the bench, in a worksheet, or in a fault report.Read guide
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Practical Wiring and Losses

A practical guide to voltage drop, wire resistance, cable sizing decisions, and the point where the wiring stops being an invisible connection and becomes part of the circuit you have to design around.

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Input guide

These are the main values the calculator uses. Keep the units consistent and, where relevant, match the assumptions explained in the related guide.

Input

Voltage

Unit: V

Use the voltage across the same component or resistive path you are analysing.

Input

Current

Unit: A

Enter the current through the component or circuit path you want to check.

Input

Resistance

Unit: ohms

Use the resistance for the same load or component as the voltage and current values.

Formulae

V = I x R
I = V / R
R = V / I

When to use this calculator

Use this page for quick DC circuit checks, troubleshooting, worksheet verification, or component selection when any two of voltage, current, and resistance are already known.

How to read the result

The main result shows the missing value first. If you fill in all three fields, the page switches to validation mode and explains whether the numbers agree with Ohm's Law.

Worked example

If a resistor has 12 V across it and 2 A flowing through it, the missing resistance is 6 ohms because R = V / I.

If you then enter all three values together, the page confirms that the set is internally consistent instead of solving again.

Assumptions and limits

This calculator applies the standard linear Ohm's Law relationship for simple resistive scenarios. It does not model AC phase effects, non-linear components, or tolerance bands.

Common questions

What happens if I enter all three values?

The page checks whether the entered voltage, current, and resistance agree within a small tolerance and shows a helpful notice if they do not.

Can I use negative values?

This page is designed for positive magnitudes in straightforward circuit calculations. If you are modelling polarity or direction, handle that separately.

When is this calculator not enough on its own?

Use a more detailed circuit analysis when reactive components, AC phase angle, temperature effects, or device tolerances materially affect the result.

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