LED Resistor Calculator

The LED resistor calculator can help you determine the appropriate resistor value for a specific LED and power supply voltage.


To find the resistor, enter the following for the LED

  • Supply Voltage (V)
  • Forward Voltage (Vf)
  • Current (I)



LED Resistor Formula

R = (V-Vf)/I

Example Calculation

The data sheet for a diode can be used to find its forward voltage and current.

For this diode, from the plot below Vf = 2 V and we use I = 5 mA.

Use these values in the calculator above to find a resistor value of 600 Ohm. Approximately 15 mW of power is dissipated in the resistor.

Referring to this datasheet, any of the resistors can be used based on the power rating information provided. For instance the smallest 0402 resistor has a rating of 63 mW which exceeds the calculated dissipation by a factor of 4.

If you cannot find the data sheet for the LED here are a couple of other methods to find the forward voltage:

  1. Examine the LED:
    • Look for any markings on the LED or its packaging. Some LEDs have the forward voltage printed on them.
  2. Use a General Guideline:
    • In the absence of specific information, you can use a general guideline. For example:
      • Red LEDs typically have a forward voltage of around 1.8 to 2.2 volts.
      • Orange and yellow LEDs typically have a forward voltage of around 1.9 to 2.2 volts.
      • Green LEDs typically have a forward voltage of around 2 to 3.1 volts.
      • Blue and White LEDs typically have a forward voltage of around 3.0 to 3.6 volts.

Note that these are approximate values, and the actual forward voltage can vary depending on the specific LED model and manufacturer.

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