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LED resistor calculator
The resistor an LED needs, with its power rating and the closest standard value.
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About LED resistor calculator
Find the series resistor that protects an LED. The formula is supply voltage minus LED forward voltage, divided by the current you want, usually 10 to 20 mA. The tool also shows the resistor's power rating and rounds to the closest standard value, such as E12 series.
How to use LED resistor calculator
- Enter your numbers above.
- The result updates instantly as you type.
- Change any value to compare different cases.
Why use this tool?
- Private: everything happens in your browser. Nothing you enter is uploaded.
- Free, with no sign-up, no watermark and no limit on how often you use it.
- Works on phones, tablets and computers: Android, iPhone, Windows, Mac and Linux. Nothing to install.
- Available in 10 languages.
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Frequently asked questions
What resistor do I need for a red LED on 5V?
A red LED drops about 2 V. At 20 mA, subtract 2 from 5 and divide by 0.02 to get 150 ohms. A 220 ohm resistor is a safe common choice.
Is LED resistor calculator free?
Yes. LED resistor calculator on Toolipedia is free to use, with no sign-up and no watermark.
Is it safe to use?
Yes. Everything is worked out in your browser, and nothing you enter is sent to our server.
Does it work on my phone?
Yes. It works in any modern browser on Android and iPhone, as well as on tablets and computers. There's nothing to install.
Do I need an account?
No. Just open the page and use the tool. There's no sign-up and no email needed.