Enter the voltage source, the voltage drop across the LED, and the current through the LED into the calculator. The calculator will display the needed resistance for the simple circuit.

LED Resistor Formula

The following formula is used to calculate the resistance of an LED circuit.

 R = (Vs - Vl)/ IL
  • Where R is the resistance
  • V is the voltage of the source
  • Vl is the voltage drop across the LED
  • IL is the current through the LED

To calculate the LED resistance, subtract the voltage drop across the LED from the voltage of the source, then divide by the current.

LED Resistor Definition

An LED resistor is defined as the total resistance in an LED circuit.

LED Resistor Example

How to calculate LED resistor

  1. First, determine the source voltage

    Measure or calculate the voltage coming from the source.

  2. Next, measure the voltage drop across the LED

    This can be done by measure directly after the LED and subtracting that value from the source voltage.

  3. Next, measure the current across the LED

    Measure or calculate the current across the LED.

  4. Finally, calculate the resistance

    Using the information from steps 1,2 and 3, calculate the LED resistance.


What is a LED resistor?

The LED resistor is the total resistance needed for a simple LED circuit in order for it to work properly.

led resistor calculator
led resistor formula