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Ohm’s law calculator

GCSEA-level Electricity

For a resistor at constant temperature, the potential difference is the current multiplied by the resistance.

V = I R

This free calculator is for GCSE and A-level physics. Choose the quantity you want to find, enter the other values with their units, and it shows the working in the layout used in exams, with the answer to the number of significant figures you choose. The values shown are an example. Change them to your own.

Quantity to find

VPotential difference to find 12.0 V

ICurrent

RResistance

Significant figures

Working

Write the equation
V = I R
Substitute the values
V = 0.5 × 24
Calculate
V = 12 V
Give the answer to 3 significant figures
V = 12.0 V

Worked example

Find V, the potential difference. Given: current I = 0.500 A; resistance R = 24.0 Ω.

Write the equation
V = I R
Substitute the values
V = 0.5 × 24
Calculate
V = 12 V
Give the answer to 3 significant figures
V = 12.0 V

Symbols and units

Symbol	Quantity	SI unit
V	Potential difference	V
I	Current	A
R	Resistance	Ω

Ohm’s law: rearranged

To find potential difference: V = I R
To find current: I = V / R
To find resistance: R = V / I

Exam tip

Use the p.d. across the same component that the current flows through.

Common questions

What is the formula for ohm’s law?

The equation is V = I R, where V is the potential difference (V); I is the current (A); R is the resistance (Ω).

What units should I use for ohm’s law?

In SI units: potential difference in V, current in A, resistance in Ω. The calculator also accepts common alternatives such as kilometres, grams or minutes, and converts them for you.

How do I rearrange V = I R?

Rearranging gives these forms: to find potential difference: V = I R. to find current: I = V / R. to find resistance: R = V / I.

Practise ohm’s law questions

Include unit conversions (km, g, minutes…)

Press the button for a question with random numbers. Work it out on paper first, then type your answer.

Read the full explanation on the Ohm’s law formula page. More electricity equations: Charge, current and time, Electrical power, Electrical power, Energy transferred, Resistors in series, Resistors in parallel, Resistivity, EMF and internal resistance. See the full list on the physics equation calculator page.