LED Series Resistor Calculator

Last Updated on January 28, 2021 by Krunal Shah (Mod)

This calculator would help you to calculate value of current limiting resistor. The resistor limits the current flowing through the LED. Over current may burn the LED.

How to use the calculator?

• For this calculator, enter the supply voltage in volts.
• Enter the forward voltage in volts. You can know the forward voltage of an LED from it’s datasheet given by manufacturer (recommended). In case you can’t find refer the below table.

• Enter the value of forward current from datasheet.
• The calculator would show automatically the calculated value.

How to calculate the value of LED Series Resistor?

You can calculate the value of LED series resistor with the help of following formula:

R = (Vs – Vf) / If

where,

R = resistor value in ohms

Vs = Supply voltage in volts

Vf = forward voltage in volts

If = forward current in mA

Example: Let us say you have supply voltage of 12 volts. The forward voltage of an LED is 2.1 volts and forward current is 30 mA. The resistor required would be 330 Ω.