LED Series Resistor Calculator
Find the series resistor for one or more LEDs from supply voltage, forward voltage and current, with the next standard E12 value and power ratings.
Runs on your device
Result
Results appear here as you type.
What it does
R = (Vsupply − n·Vf) / I. The exact value is rarely available, so the calculator rounds up to the next E12 resistor (which slightly lowers the current, the safe direction) and recalculates.
How to use it
- Enter the supply voltage.
- Enter the LED forward voltage and current from its datasheet.
- Enter how many LEDs are in series.
Example
(5 − 2) / 0.02 = 150 Ω, already an E12 value. Select Try an example above to see it.
When it helps
- Arduino and ESP32 indicator LEDs.
- LED strips and panels.
- Electronics lab exercises.
Questions
Typical forward voltages?
Red ≈ 2.0 V, yellow ≈ 2.1 V, green ≈ 2.2 to 3.2 V, blue and white ≈ 3.0 to 3.3 V. Check your datasheet.
Which resistor wattage should I buy?
At least double the calculated dissipation; 1/4 W is fine below about 125 mW.
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