# Choosing the correct resistor for your LED

**URL:** <https://forum.digikey.com/t/choosing-the-correct-resistor-for-your-led/183>\
**Category:** Digikey.com Navigation and Terminology\
**Tags:** navigation-tips\
**Created:** [April 19, 2017, 2:13pm UTC](https://forum.digikey.com/t/choosing-the-correct-resistor-for-your-led/183 "2017-04-19T14:13:05Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Robert\_Fay](https://sea2.discourse-cdn.com/digikey/user_avatar/forum.digikey.com/robert_fay/32/6529_2.png) [@Robert\_Fay](https://forum.digikey.com/u/Robert_Fay)\
**Post date:** [April 19, 2017, 2:13pm UTC](https://forum.digikey.com/t/choosing-the-correct-resistor-for-your-led/183/1 "2017-04-19T14:13:05Z")

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Choosing the correct resistor value is imperative to insure your LED receives proper voltage and current. To ensure you have the correct resistor you will need to know three values from your circuit.

Vs - Supply Voltage - This is the power supply that you are using to power your circuit.  
Vf - Forward voltage for your LED. This is the voltage required to turn on your LED.  
If - Forward Current for your LED. This is the current required by your LED for operation.

With these numbers you can calculate the resistance (R) required with the following equation.  
R = (Vs - Vf) / If

For my example I am going to use LED part [67-2250-ND](https://www.digikey.com/short/3wv0mw). This LED has a forward voltage of 3.2V and a forward current of 20mA. I will be powering my circuit with a 9V battery.

R=(9V-3.2V)/.020A  
R= 290ohms

Next you will want to make sure you calculate the wattage required for your resistor to ensure that your resistor can handle the load. Using Ohm’s law you can verify the voltage that is being dropped across your resistor.  
Resistance x Current = Voltage in my example would be 290ohm x .020A = 5.8V  
To calculate power you would then take Volts x Amps = Watts. In our example this would be 5.8V x .020A = .116W  
So the required resistor for my example circuit would be 290ohms and 1/8th watt.

To help simplify the process DigiKey has an [LED Series Resistor Calculator](http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-led-series-resistor) that will calculate you required resistance and power ratings for your LED circuit.  
[![image](https://global.discourse-cdn.com/digikey/original/2X/4/4d94bb6b212fd833aaca34b3f795a57c793cecb2.png)](http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-led-series-resistor)

DigiKey also has a separate [Ohm’s Law Calculator](http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-ohms) for  
customer convenience.  
[![image](https://global.discourse-cdn.com/digikey/original/2X/c/c76a7a5557650f9ee41c8f134eaa48080a5cf45b.png)](http://www.digikey.com/en/resources/conversion-calculators/conversion-calculator-ohms)

Here’s a video take on the topic if you would like to check it out.

[![](https://global.discourse-cdn.com/digikey/original/3X/3/7/372731f410e8b2e83bae89498156e12e172176b1.jpeg "YouTube") ](https://www.youtube.com/watch?v=UWx2BEx7xyI)

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<div class="post-metadata">

**Author:** ![manikarni](https://avatars.discourse-cdn.com/v4/letter/m/a6a055/32.png) [@manikarni](https://forum.digikey.com/u/manikarni)\
**Post date:** [December 8, 2017, 11:54am UTC](https://forum.digikey.com/t/choosing-the-correct-resistor-for-your-led/183/2 "2017-12-08T11:54:39Z")

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Yes these DigiKey calculators are very useful.  
But this LED resistor calculator could have more options like selecting No. of LEDs if more than 1 LED is connected and could have prefilled voltages for commonly used LEDs like this [LED resistor calculator](https://circuitdigest.com/calculators/led-resistor-calculator) has.  
Even some LED resistor calculators are very cool and they will show you nearest available resistor value for your circuit and also show you color coding of calculated resistor like [http://ledcalc.com/](http://ledcalc.com/)