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Ohm's Law Calculator

Solve V = I × R for voltage, current or resistance — enter any two values and get the third, plus the power dissipated (P = V×I).

 

Formula

$$ V = I\,R \qquad I = \frac{V}{R} \qquad R = \frac{V}{I} \qquad P = V\,I $$

Worked example

A 12 V supply across a 24 Ω resistor draws \( I = V/R = 12/24 = 0.5\ \text{A} \) and dissipates \( P = VI = 12 \times 0.5 = 6\ \text{W} \).

How it works

Ohm's law states that the current through a conductor is proportional to the voltage across it and inversely proportional to its resistance: V = I R. Rearranged, I = V/R and R = V/I.

Enter any two of the three quantities and the calculator finds the missing one and the electrical power P = VI (equivalently I²R or V²/R). Voltage is in volts, current in amperes and resistance in ohms (Ω).

Frequently asked questions

What is Ohm's law?

Ohm's law is V = I R: the voltage across a resistor equals the current through it multiplied by its resistance. It applies to ohmic (linear) components at constant temperature.

How do you calculate current from voltage and resistance?

Current is I = V / R. Set 'Solve for' to Current, enter the voltage and resistance, and the calculator returns amperes.

How do you find power using Ohm's law?

Power is P = V I, which also equals I²R or V²/R. This calculator shows the power automatically alongside the answer.

What are the units in Ohm's law?

Voltage is measured in volts (V), current in amperes (A) and resistance in ohms (Ω). Power comes out in watts (W).

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