Calculate electrical values using Ohm's Law (V=IR) and power equations. Find voltage, current, resistance, or power from any two known values.
Enter any two values to calculate the others
You might also find these calculators useful
Calculate power factor, real, reactive, and apparent power
Calculate energy consumption, battery life, and electricity costs
Calculate output voltage, resistor values, and power dissipation
Calculate equivalent resistance for series and parallel circuits
Ohm's Law and power equations form the foundation of electrical engineering. Our calculator lets you find any unknown value (voltage, current, resistance, or power) when you know two others.
Ohm's Law states that the current through a conductor is directly proportional to the voltage and inversely proportional to the resistance. Combined with power equations, you can calculate any electrical parameter.
Ohm's Law & Power Formulas
Calculate resistor values for LED current limiting.
Determine voltage drop and power dissipation.
Calculate current to select appropriate wire gauge.
Estimate runtime from power consumption and capacity.
Instantly calculate missing values in electrical circuits.
Determine proper resistor values and power ratings.
Verify current draw doesn't exceed wire or component ratings.
Voltage is measured in Volts (V), current in Amperes (A), resistance in Ohms (Ω), and power in Watts (W). The calculator handles conversions between milli, kilo, and mega prefixes.
For AC circuits, Ohm's Law uses impedance (Z) instead of resistance, which includes capacitive and inductive reactance. This calculator is designed for DC and purely resistive AC circuits.
Calculate the power dissipation using P = I²R or P = V²/R, then choose a resistor rated for at least 2x the calculated power for safety margin.
All formulas are mathematically equivalent. V = IR can be rearranged to I = V/R or R = V/I. Power formulas P = VI, P = I²R, and P = V²/R all give the same result.