EMBEDDED TOOL
LED Series Resistor Calculator
Find the current-limiting resistor needed to safely drive one or more LEDs.
Required resistor
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Nearest standard value (E12)
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Power dissipated / recommended rating
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About this tool
Work out the current-limiting resistor needed to drive one or more LEDs safely from a given supply voltage, using R = (Vsupply − N×Vf) ÷ If. Also rounds up to the nearest standard E12 resistor value and suggests a power rating so the resistor doesn't overheat.
Frequently asked questions
- Why round up to the nearest standard value instead of down?
- Rounding up keeps the LED current at or slightly below its rated forward current — rounding down would push more current through the LED than intended, shortening its life or damaging it.
- What forward voltage should I use for my LED?
- It depends on color: roughly 1.8–2.2V for red/yellow, 3.0–3.4V for white/blue/green LEDs — check the datasheet if you have one, since exact values vary by manufacturer.
- How is the power rating recommended?
- The exact power dissipated (P = I²R) is rounded up to the next common resistor wattage (1/8W, 1/4W, 1/2W, 1W, 2W) with headroom, since running a resistor at its exact rated power tends to shorten its life.