FluxBench

LED Series Resistor Calculator

v1.0 calculator

Calculate the correct resistor value for LED circuits

LED Series Resistor Calculator
Add a series resistor before an LED to limit current (Vs → resistor → LED → GND).
This calculates the resistor value and how much power it will burn as heat.
Formula: -
Computed: -
Resistor Heat Generated: -
E6 nearest: -
E12 nearest: -
E24 nearest: -
E48 nearest: -

LED Series Resistor Calculator

Calculate the correct Resistor value to limit Current through an LED.

How to use

Enter the following values:

  • Supply Voltage (V) - The power supply voltage
  • LED Forward Voltage (V) - The forward voltage drop of the LED (typically 1.8-3.3V)
  • LED Current (mA) - The desired current through the LED (typically 10-30mA)

The calculator will determine the required Resistance and suggest the nearest standard resistor value.

Examples

Example 1: Standard Red LED

  • Supply: 5V
  • LED Forward Voltage: 2.0V
  • Current: 20mA
  • Result: 150Ω resistor

Example 2: High-Power LED

  • Supply: 12V
  • LED Forward Voltage: 3.3V
  • Current: 30mA
  • Result: 290Ω resistor (use 270Ω standard)

FAQ

Q: What if my LED doesn’t have a forward voltage listed? A: Most standard LEDs are 1.8-2.2V (red/yellow) or 3.0-3.3V (blue/white). Check the datasheet for your specific LED.

Q: Can I use a higher value resistor? A: Yes, but the LED will be dimmer. Using a lower value may damage the LED.

Q: What about multiple LEDs? A: For series LEDs, add their forward voltages together. For parallel LEDs, calculate each branch separately.