How to use this calculator
- Enter the supply voltage and LED forward voltage.
- Enter the desired LED current in milliamps.
- Use the recommended standard resistor with at least the shown power rating.
Example
A 5 V supply, 2 V red LED and 20 mA current require 150 Ω. The resistor dissipates 0.06 W.
How it works
Calculate the required LED series resistor, power dissipation and a safe standard recommendation. Inputs are calculated directly in your browser and the result updates whenever a value changes.
Frequently asked questions
Why choose a higher resistor value?
A slightly higher standard value reduces current and is safer for the LED.
Can I connect several LEDs in parallel with one resistor?
Use one resistor per parallel branch so current shares predictably.