⚡ EE Calcs

LED Series Resistor Calculator

Find the resistor value for any LED and supply voltage.

VS R LED (Vf) I series loop: VS → R → LED → GND · I = (VS − Vf)/R

Values

Result

R = 150 Ω · P = 60 mW

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.