LED Series Resistor Calculator
Find the right current-limiting resistor for any LED in seconds — includes E12 standard value and power dissipation.
Calculated resistor
150 Ω
Nearest E12 value
150 Ω
Power dissipation
60 mW
(60.0 mW)
Formula
R = (Vsupply − Vforward) / I
Pick the nearest standard (E12) value at or above this for safety.
Why an LED needs a series resistor
An LED is a diode: above its forward voltage its current rises almost vertically, so connecting it straight across a supply lets current run away and burns it out. A series resistor drops the leftover voltage and fixes the current at a safe level.
The diagram lights up when your supply exceeds the LED's forward voltage — the condition needed for it to conduct at all.
Typical values
- Red / yellow LEDs: Vf ≈ 1.8–2.2 V. Blue / white LEDs: Vf ≈ 3.0–3.4 V.
- Indicator brightness is fine at 5–10 mA; 20 mA is a common 'full' rating — don't exceed the datasheet max.
- Always round the resistor up to the next standard value: more resistance means slightly less current, which is safe.
- Check the power rating — most builds are well under the ¼ W a standard resistor handles.
Where it's used
Status LEDs on Arduino/ESP32 projects, panel indicators, and any single LED driven from a microcontroller pin or battery.