LED circuit calculator

A calculator to find what value you need for a resistor if you want to connect a LED to a power source (battery, power supply, mains etc).


Formula used: R = (VS - VLED) / ILED, where VS = Source Voltage, VLED = LED's Forward Voltage, ILED = LED's forward current
The typical circuit looks like:
Circuit resistor-LED

The LED forward voltage and LED forward current can be easily found in the LED's datasheet. But, if you do not have the datasheet you can take these default values:
Colour Forward Voltage (in V)
Infrared (IR) 1.5
Red 2
Orange 2
Yellow 2.1
Green 2.2
True Green (530–550 nm) 3.3
Blue 3.3
Violet / Royal Blue (430 nm) 4.6
White 3.3
Ultraviolet (UV) 3.3