Ohm's Law Calculator for Voltage, Current, Resistance

Ohm's Law is the single most important relationship in electronics. Formulated by German physicist Georg Simon Ohm in 1827, it states that the current flowing through a conductor between two points is directly proportional to the voltage across them and inversely proportional to the resistance. In its familiar form, V = I × R, where V is voltage in volts, I is current in amperes, and R is resistance in ohms (Ω). This compact equation lets you find any one quantity when you know the other two, which is why it underpins virtually every circuit calculation engineers, technicians, and hobbyists perform. The Ohm's Law calculator extends the core relationship with the electrical power formula, P = V × I, measured in watts. Combining the two relationships gives a family of equivalent expressions: P = I² × R and P = V² / R. Together, the four quantities — voltage, current, resistance, and power — form a closed system in which knowing any two lets you derive the remaining two. Enter exactly two values and the Ohm's Law calculator picks the correct formulas automatically, so you never have to remember which rearrangement to use. The math behind each case is straightforward. If you know voltage and current, resistance is V ÷ I and power is V × I. If you know voltage and resistance, current is V ÷ R and power is V² ÷ R. If you know current and resistance, voltage is I × R and power is I² × R. When power is one of your known values, the calculator uses square roots where needed — for example, with resistance and power known, current is √(P ÷ R) and voltage is √(P × R). Every result is computed in double-precision arithmetic and rounded for readability. Understanding what the numbers mean is as useful as computing them. Voltage is the electrical pressure pushing charge through a circuit; current is the rate of charge flow; resistance opposes that flow and converts electrical energy into heat; and power is the rate at which energy is delivered or dissipated. A resistor's power rating, an LED's series resistor, a battery's runtime, and a motor's load can all be analysed with these four quantities. Picking a resistor with a high enough wattage rating, for instance, depends directly on the P = I² × R you calculate here. Typical uses include sizing current-limiting resistors for LEDs, checking that a resistor won't overheat, estimating how much current a load draws from a battery or power supply, designing voltage dividers, and troubleshooting circuits where a measured value doesn't match expectations. Note that Ohm's Law applies to ohmic (linear) components at constant temperature; semiconductors, lamps, and other non-linear devices only follow it approximately, so treat the results as ideal-case estimates for real components.