Ohms Law Calculator - Voltage, Current, Resistance & Power

About Ohm's Law

Ohm's Law is one of the most fundamental relationships in electrical science. It states that the electric current flowing through a conductor between two points is directly proportional to the voltage across those two points, and inversely proportional to the resistance of the conductor: V = I × R. In plain terms, doubling the voltage doubles the current; doubling the resistance halves it.

The law is named after the German physicist Georg Simon Ohm (1789–1854), who published his findings in Die galvanische Kette, mathematisch bearbeitet (1827). Ohm derived the relationship experimentally using early voltaic cells and wires of varying thickness and length — painstaking work at a time when even measuring current precisely was difficult. His conclusions were initially met with skepticism by the scientific establishment, but within two decades they were universally recognized, and the unit of electrical resistance was named the ohm (Ω) in his honor.

The power extension — P = V × I — follows naturally from the definition of work done per unit time by an electric field, and together with Ohm's Law gives the full set of twelve formulas relating V, I, R, and P shown in the table above. These four quantities govern virtually every practical circuit calculation, from choosing the right resistor to protect an LED, to sizing a power supply for a motor, to understanding why thin extension cords overheat. Ohm's Law is as indispensable to an electronics engineer as Newton's laws are to a mechanical one.