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LED resistor calculator
The resistor an LED needs to run safely at its rated current, rounded to a value you can actually buy.
150 Ω
nearest standard value · ideal was 150 Ω
Runs the LED at 20.0 mA, dissipating 0.060 W
Use a 125 mW resistor or larger
R = (supply − LED forward drop) ÷ current. Rounded up to the nearest E12 value, which under-drives the LED slightly rather than over-driving it — the safe direction to round.