Ohm's Law Calculator — Voltage, Current, Resistance & Power Solver
This free ohms law calculator solves Ohm's Law circuits instantly. Calculate voltage, current, resistance, or power given any two values. Handles metric prefixes and evaluates resistor wattage ratings for safe circuit design.
Circuit Values
Ohm's Law requires exactly two input values to calculate the other two. Fill in two fields, and leave the other two blank.
Resistor & Circuit Outputs
Ohm's Law Calculated Results
Voltage (V)5.000 V5 V
Current (I)20.00 mA0.02 A
Resistance (R)250.00 Ω250 Ω
Power (P)100.00 mW0.1 W
Resistor Wattage Rating Recommendation
Use at least a 1/8 Watt (0.125W) resistor.
Formula Derivation & Calculations
1. Given: Voltage = 5 V (5 V)
Given: Current = 20 mA (0.02 A)
2. Calculate Resistance: R = V / I = 5 / 0.02 = 250.000000 Ω
3. Calculate Power: P = V * I = 5 * 0.02 = 0.100000 W