LED Resistor Calculator

Calculate the current-limiting resistor needed for an LED.

Supply Voltage (Vs)

LED Forward Voltage (Vf)

LED Current (I)

Required Resistor

300 Ω

Nearest E24: 300 Ω

Power dissipation: 3.0 mW

Resistor rating needed: 1/8 W is fine

Typical LED Forward Voltages

Color	Vf (typ)	If (typ)	Notes
Red	1.8 - 2.2V	20mA	Most efficient
Orange	2.0 - 2.2V	20mA
Yellow	2.0 - 2.2V	20mA
Green	2.0 - 3.2V	20mA	Wide range
Blue	3.0 - 3.5V	20mA	Higher voltage
White	3.0 - 3.5V	20mA	Blue + phosphor
IR	1.1 - 1.5V	20-100mA	Invisible
UV	3.3 - 4.0V	20mA	Needs 5V+ supply

Single LED: $R = \frac{V_s - V_f}{I}$
Multiple LEDs in series: $R = \frac{V_s - n \cdot V_f}{I}$ where $n$ is the number of LEDs

Brightness control: LED brightness is roughly proportional to current. 5mA = dim indicator, 20mA = bright.