💡

LED Series Resistor

Calculate the series resistor for a single LED. Given supply voltage, LED forward voltage, and desired forward current, returns the required resistance, nearest E12 standard value, and recommended power rating.

Supply voltage (V)

LED forward voltage Vf (V)

LED forward current If (mA)

Limitations: Single-LED series-resistor topology. For LEDs in parallel, use separate resistors per LED. For constant-current driving (better for high-power LEDs), this tool is not appropriate.

What to do next: Standard 5mm indicator LEDs: Vf ≈ 1.8–2.1V (red), 3.0–3.4V (blue/white), If = 20mA. High-brightness LEDs: check the datasheet; If often 100–350mA.