LED Resistor Calculator

Created by Bogna Szyk
Reviewed by Małgorzata Koperska, MD and Jack Bowater
Last updated: Feb 05, 2022

This LED resistor calculator is a tool for determining what resistor you should use when creating different electronic circuits with LEDs. Thanks to these calculations, you can be sure that you won't damage the diodes with an excessive current.

You can use this LED calculator to find both the required resistance and the power dissipation in a single LED, all LEDs, or in the resistor.

LED calculator: an overview

LEDs, or light-emitting diodes, are small electronic components. When current is applied to LEDs, they emit light in various colors, such as red, green, or blue. If the current passing through the diode is too high, though, it will damage the LED.

LED resistor

To limit the current passing through the diode, it's common practice to add a resistor to the circuit, as shown in the image above image. This resistor is usually added in series. Even though this method is simple and solves many problems with a basic circuit, it shouldn't be applied for high-current LEDs.

What do you need to know?

In order to calculate the resistance and power dissipation, you need to input a few parameters into this LED resistor calculator:

  • Circuit type. Are your LEDs connected in series or in parallel?

  • n - number of connected LEDs.

  • V - supply voltage of your circuit. Typical values are 5, 7 and 12 volts for molex connectors and 1.5 or 9 volts for batteries.

  • Vₒ - voltage drop across one LED. This value depends on the LED color and ranges from 1.7 volts (infrared) to 3.6 (white or blue diodes).

  • Iₒ - current across one LED. Regular LEDs require 20 or 30 mA.

LEDs in series

If you connect a few diodes in series, or are calculating the resistor for just one diode, you can use the formulas listed below:

  1. Resistance: R = (V - n * Vₒ) / Iₒ

  2. Power dissipated in a single LED: Pₒ = Vₒ * Iₒ

  3. Power dissipated in all LEDs (total): P = n * Vₒ * Iₒ

  4. Power dissipated in the resistor: Pr = (Iₒ)² * R

LEDs in parallel

For LEDs connected in parallel, the LED resistor calculator uses the following equations:

  1. Resistance: R = (V - Vₒ) / (n * Iₒ)

  2. Power dissipated in a single LED: Pₒ = Vₒ * Iₒ

  3. Power dissipated in all LEDs (total): P = n * Vₒ * Iₒ

  4. Power dissipated in the resistor:Pr = (n * Iₒ)² * R

Wondering where these formulas come from? Take a look at the Ohm's law calculator!

Bogna Szyk
LEDs connected in...
series
Number of connected LEDs
Supply voltage
V
Current through the LED
mA
LED color
Red
Voltage drop across LED
V
Resistance
Ω
Power dissipation
In a single LED
MW
In all LEDs
MW
In the resistor
MW
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