LED Series Resistor Calculator
Find the resistor value for any LED and supply voltage.
How to size an LED resistor
An LED has roughly constant forward voltage (Vf) once conducting, so the resistor must drop the remaining supply voltage and set the current: R = (Vs − Vf) / I. Typical forward voltages: red 1.8–2.2 V, green 2.0–3.2 V, blue/white 2.8–3.6 V.
Check the resistor's power dissipation too: P = I²·R. A ¼ W resistor is fine for most indicator LEDs below about 20 mA.
Values
Result
R = 150 Ω · P = 60 mW