Ohm’s Law Calculator

Calculate voltage, current, resistance, and power for simple electrical circuits. Ohm’s Law is most useful for resistive loads or circuit sections where voltage, current, and resistance have a stable linear relationship.

How to use this calculator

Choose Solve for voltage, current, or resistance. Enter the other two values and choose their units. The form accepts V, mV, kV, A, mA, microamps, ohms, kilohms, and megohms, then returns the missing value plus voltage, current, resistance, and power.

Core Formulas

Ohm’s Law is:

$V = I \times R$

Power can be found from:

$P = V \times I$

You can rearrange these formulas to solve for the missing value when two values are known. For example, a 12 V supply across a 6 ohm resistor produces 2 A of current and dissipates 24 W of power.

Practical uses

Use the result to size resistors, estimate battery current draw, check a power supply, or troubleshoot a circuit section. Always compare calculated power with component ratings and leave a safety margin. Related tools include the electric current converter, power converter, and decibel calculator.

Common mistakes

• Mixing milliamps and amps without converting.
• Applying the formula to nonlinear devices without the right model.
• Ignoring power dissipation and heat.