Wiring & Power Calculators

Ohm's law is four equations people re-derive badly under pressure — enter any two of voltage, current, resistance and power here and the rest solve live, with a resistor power-rating check so you do not specify a component that will cook.

Voltage drop is the one that catches out long runs: a circuit that is fine at ten metres can be out of spec at forty, and undersized cable is a fire risk rather than an inconvenience. Calculators inform, codes govern — wiring work must follow your local electrical code and, in most places, be done or inspected by a licensed electrician.