LEDs burn out without a current-limiting resistor. This tool tells you exactly which resistor to use for any LED color and supply voltage.
Leave blank to use typical value for selected color
Max: 30mA — typical: 20mA. Use 10–20mA for normal brightness.
Exact Resistor
R = (Vs − Vf) / If = (5 − 2) / 20mA
Nearest Standard E24 Value — use this one
→ actual If = 20.0mA · resistor dissipates 60mW · use ≥ ¼W (250mW) rated resistor
Resistor power
60 mW
LED power
40 mW
Why this matters
Without a resistor, an LED connected to 5V draws hundreds of mA — it burns out in seconds and can damage your Arduino pin. A 220Ω or 330Ω resistor is the #1 most used component in beginner projects for exactly this reason.