Calculator and formulas for calculating the LED series resistor
LEDs are usually operated via a series resistor. The series resistor must be dimensioned in such a way that the supply voltage and the maximum permissible current are not exceeded. You can calculate the size of the resistor on this page.

\(\displaystyle V_S \) Source voltage
\(\displaystyle V_D \) LED voltage
\(\displaystyle I_D \) Maximum LED current
\(\displaystyle R_V \) Serial resistance
\(\displaystyle P_V \) Serial resistance power rating
Serial resistance  \(\displaystyle R_v=\frac{V_S  V_D}{I_D}\)  
Serial resistance power rating  \(\displaystyle P_v=(V_S  V_D) · I_D\)  \(\displaystyle =I_D^2 · R_v\) 
