Ohm's Law Calculator
How to use Ohm's law
- Enter any two of voltage, current, resistance and power.
- Leave the other two empty.
- The missing values appear with SI prefixes such as mA and kΩ.
Frequently asked questions
What are the formulas?
V = I × R and P = V × I, so P = I² × R = V² / R.
What current flows through 100 Ω at 12 V?
12 / 100 = 0.12 A, or 120 mA, and the resistor dissipates 1.44 W.
Why does the power matter?
A resistor has to be rated for the power it dissipates. A common rule is to choose one rated for about twice the calculated power.
More engineering calculators
Resistor Color Code CalculatorVoltage Divider CalculatorLED Resistor CalculatorSeries and Parallel CalculatorGravel CalculatorWallpaper CalculatorRC Time Constant CalculatorSolar Panel CalculatorMore engineering calculators (43)
Exam courses
Related simulations
Electric Field SimulatorRC and RL Circuit SimulatorSeries and Parallel Circuit SimulatorElectromagnetic Induction Simulator
Guides
How to Read Resistor Color CodesHow to Choose a Resistor for an LEDHow to Calculate Voltage Drop in a CableHow a Voltage Divider WorksHow to Use Ohm's LawHow to Convert kW to AmpsWhat Is an RC Time Constant?Series and Parallel Circuits ExplainedHow Electromagnetic Induction Works: Faraday's Law, Lenz's Law, Generators and TransformersElectric circuits: study guide