Ohm's law calculator

Use any two of voltage, current, resistance and power to solve V = IR and P = VI for a passive DC resistor.

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First known value

Second known value

More inputs and assumptions

Known pair (units in this order)

Answer

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Use any two of voltage, current, resistance and power to solve V = IR and P = VI for a passive DC resistor.

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Precision and calculation record

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Rounding changes displayed numbers, not the calculation. Text, fractions, matrices and CSV schedules keep their own formatting. Automatic keeps up to 12 significant digits, with money shown to cents where applicable.

Saved scenario

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Formula and assumptions

Enter nonnegative magnitudes for an ideal ohmic load. No AC power factor, reactance, nonlinear components, temperature effects or resistor color bands. Zero values that make the pair indeterminate fail explicitly. The result does not choose a component rating, conductor or safe circuit design.

Automatic precision shows numbers to 12 significant digits. Thousands separators such as 1,000 are accepted; use a dot for decimals.

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Updated 2026-09-29

Using Ohm's law calculator

Use any two of voltage, current, resistance and power to solve V = IR and P = VI for a passive DC resistor.

Next: Voltage calculator

Next: Electrical load calculator

A worked example

For first known value = 12, second known value = 3, known pair (units in this order) = Voltage V, current A, voltage (v) = 12.

Before you use the result

Example results for first known value

These examples use Second known value: 3; Known pair (units in this order): Voltage V, current A. They are reference calculations, not recommended settings.

First known value	Voltage (V)
6	6
12	12
24	24

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