Electronics
Ohm's law for any two of voltage, current, resistance and power, voltage drop along a cable, and resistor colour codes both ways.
Ohm’s Law Calculator
Voltage, current, resistance and power from any two of them, all six combinations, by Ohm’s law and the power relationships.
Voltage Drop Calculator
The voltage lost along a copper or aluminium cable for a given current and run length, single phase, three phase or DC, and what reaches the load.
Resistor Colour Code Calculator
A resistor’s value and tolerance range from its colour bands, or the bands for a value, snapped to the nearest E12, E24 or E96 preferred value.
Voltage Divider Calculator
The output of a two-resistor voltage divider, or the resistor or input voltage that gives the output you need, with the current, the power in each resistor and an optional load.
Series and Parallel Resistor Calculator
The total resistance of up to 12 resistors in series or in parallel, and the current and power they take from a supply voltage if you give one.
LED Resistor Calculator
The series resistor for one LED or a string of them, from the supply voltage and the forward voltage and current on the LED’s datasheet, rounded up to a standard value.
AC Power Calculator
Real, apparent and reactive power for single-phase or balanced three-phase AC from volts, amps and power factor, or the current a load of known watts draws.
Lumens to Lux Calculator
Lux and foot-candles from a light’s lumens spread over an area or in a beam, or the lumens needed for a lux level you choose.
AWG Wire Calculator
The diameter, cross-section and resistance of an American Wire Gauge size, from 4/0 to 40, or the nearest gauge to a diameter or a mm² area.
Ohm's law ties voltage, current and resistance together, and power follows from any two of them, so the Ohm's law calculator works from whichever pair you know, all six of them, and says so plainly when a zero resistance means a short circuit instead of printing infinity. Voltage drop is the same law applied to a long cable: the current goes out and comes back, so a single-phase run drops voltage over twice its length, and a three-phase run over the square root of three times it. Conductor resistance comes from the metal's resistivity and the wire's area, and the American Wire Gauge is itself defined by a formula, so no gauge table is copied in. The resistor colour code reads bands to a value with its tolerance range, and a value back to bands. None of these pages sizes a conductor or checks anything against an electrical code; ampacity, derating and local rules govern that.