LED resistor calculator
The series resistor for any LED and supply, rounded up to a value you can actually buy, with the real current and a warning if it will cook.
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Calculated
300 Ω
(Vs − Vf) ÷ I
Fit this one
300 Ω
Nearest preferred value at or above the calculation — rounding up means slightly less current, never more.
Actual current
10 mA
What the LED will really draw with that resistor.
Resistor power
30 mW
Where this comes from
The number is the easy part. If you have to explain it to a panel, read the write-up — it goes through the formula, the assumptions and the mistakes that make the answer wrong.
LEDs and the series resistorWhy an LED needs a resistor, how to calculate it for any supply voltage, forward voltages by colour, and the mistakes that kill LEDs and microcontroller pins.Other calculators
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