Ohm's Law Calculator
Input any two known principles (Voltage, Current, Resistance, or Power) and we will automatically solve for the missing variables.
Ohm's Law & Power Equation
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Understanding Ohm's Law and Power Equations
Ohm's law is the foundational mathematical principle of electrical engineering. Developed by Georg Simon Ohm in 1827, it defines the strict relationship between current, voltage, and resistance in an ideal conductor.
The Core Variables
- Voltage (V) or (E): Measured in Volts. The "electrical pressure" pushing electrons through the circuit from a power source.
- Current (I): Measured in Amperes (Amps). The actual flow rate or an amount of electrons moving through a point across the circuit per second.
- Resistance (R): Measured in Ohms (Ω). The friction or physical opposition to the current flow in the circuit.
- Power (P): Measured in Watts (W). The actual rate at which electrical energy is transferred, created, or dissipated (e.g. as heat or light).
The Formulas
Using simple algebra, if you know any two of the values above, our calculator discovers the other two. The core equations to memorize are:
- V = I × R (Voltage equals Current times Resistance)
- P = V × I (Power equals Voltage times Current)
From those two simple equations, the rest can be derived mathematically. For example, if you know Voltage and Resistance and want to find Power, you substitute $I$ with $V/R$ to get: P = V² / R.
Usage Warnings
Ohm's Law applies precisely to DC (Direct Current) circuits containing purely resistive loads. In AC (Alternating Current) systems dealing with inductors and capacitors, "Resistance" becomes complex "Impedance" (Z), and phase angles must be considered for accurate power calculations.