What Resistor Do I Need for an LED on 12 V?

Answer
560 Ω red LED, 20 mA

A standard red LED drops about 2.0 V, so on 12 V the resistor has to drop 10.0 V. At 20 mA that is 10.0 ÷ 0.020 = 500 Ω; the next standard E12 value is 560 Ω, which gives 17.9 mA and dissipates 179 mW in the resistor. A 1/2 W resistor (or larger) is enough.

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V
mA
Standard 5 mm LEDs: 10–20 mA. Check the datasheet's max current.
V
From the LED datasheet (Vf at your current).
Standard series
Resistor to use
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How we calculated this

    For estimating and educational purposes only. Results are approximate and are not a substitute for a licensed professional, the manufacturer's instructions or your local code. Disclaimer

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    LED resistor on 12 V by color (20 mA, E12 values)

    LEDVf (typ.)Exact RE12 resistorCurrentResistor power
    Red2.0 V500 Ω560 Ω17.9 mA179 mW
    Orange2.0 V500 Ω560 Ω17.9 mA179 mW
    Yellow2.1 V495 Ω560 Ω17.7 mA175 mW
    Green (standard)2.2 V490 Ω560 Ω17.5 mA172 mW
    Green (bright/true green)3.2 V440 Ω470 Ω18.7 mA165 mW
    Blue3.2 V440 Ω470 Ω18.7 mA165 mW
    White3.2 V440 Ω470 Ω18.7 mA165 mW

    Typical forward voltages; check your LED's datasheet. Rounding up to the next standard value keeps the current at or just below 20 mA.

    Frequently asked questions

    What resistor for a white or blue LED on 12 V?

    About 440 Ω exact at 20 mA (Vf ≈ 3.2 V), so use 470 Ω.

    How many red LEDs can I put in series on 12 V?

    As a rule of thumb keep at least 1 V across the resistor: 5 red LEDs in series (10.0 V in total) with 100 Ω at 20 mA.

    Can I use a bigger resistor?

    Yes. A larger value just lowers the current and brightness; most modern LEDs are clearly visible at 5–10 mA.

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