Ohm's law calculator

Type any two values with their units, like `12V, 2A`, `9V, 470R`, `20mA, 4.7k` or `60W, 230V`. The other two come back, with the formula used. V is volts, A amps, Ω (or R, or ohms) resistance, and W watts. Prefixes work too: mA, kΩ, MΩ, mW.

Any pair works. Two of the same kind, like two voltages, doesn't, because there's nothing to work out from it.

Ohm's law is V = I × R: the voltage across a resistance is the current times the resistance. Rearranged, I = V ÷ R and R = V ÷ I.

Power brings in the fourth. P = V × I, and substituting Ohm's law gives P = I² × R and P = V² ÷ R. With any two of the four you can reach the others in one or two steps, which is what the working shows. 12 V across 6 Ω draws 2 A and dissipates 24 W.

Georg Ohm published the law in 1827, in Die galvanische Kette, mathematisch bearbeitet, The Galvanic Circuit Investigated Mathematically. It was coldly received, and Ohm found so little support from the college where he taught that he resigned. Fourteen years later, in 1841, the Royal Society awarded him its Copley Medal, and in 1881 his name became the unit of resistance.