This LED resistor calculator finds the correct series resistor for an LED using R = (Vsupply − VLED) / I. Enter the supply voltage, the LED forward voltage and the desired current.
LED Resistor Calculator
Formula
R = (Vsupply − VLED) / I
How to Use This Calculator
- Enter the supply voltage.
- Enter the LED forward voltage (typically 1.8–3.3 V).
- Enter the desired LED current in mA and click Calculate.
Worked Example
For a 5 V supply, a 2 V LED at 20 mA: R = (5 − 2) / 0.02 = 150 Ω.
Frequently Asked Questions
How do you calculate the resistor for an LED?
Use R = (supply voltage minus LED forward voltage) divided by the LED current in amperes.
Why does an LED need a series resistor?
The resistor limits the current through the LED to a safe value, preventing it from burning out.
What is a typical LED current?
Most standard LEDs are run at about 20 mA, though many can operate from 5 to 20 mA.