LED resistor calculator
Work out the right resistor for one or more LEDs in series: enter the supply voltage and the LED voltage and current, and see the resistance, the standard value and the power rating.
How to useWhich resistor to use with an LED
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LED resistor calculator: what it is for
Enter the supply voltage, the LED color or voltage, the current and how many LEDs are in series. The calculator shows the calculated resistor, the next standard E24 value, the minimum power rating of the resistor and the actual current through the LED.
How to use
- Type the supply voltage.
- Choose the LED and the current.
- Use the standard resistor shown.
When to use it
- Connecting an LED to an Arduino or to 12 V.
- Building LED strips and panels.
- Avoiding burnt-out LEDs.
Frequently asked questions
How do I calculate an LED resistor?
Subtract the LED voltage from the supply voltage and divide by the current: R = (Vsupply − n × VLED) ÷ I. With 12 V, a 2 V red LED and 20 mA, the resistor is 500 Ω, and the next standard value up is 510 Ω.
What is the voltage of each LED color?
Typical values: red and yellow 1.8 to 2.2 V, green 2 to 3.2 V, blue and white 3 to 3.4 V. Check your LED's datasheet.
Why use the next standard value up?
A slightly larger resistor reduces the current and brightness a little, but protects the LED. A smaller value can exceed the maximum current and burn it out.
Is it really free?
Yes, 100% free. No sign-up, no subscription and no usage limits. All Tools123 tools are free and run right in your browser.