LED Series Resistor Calculator

The series resistor to run an LED safely — value, the nearest standard resistor and the power it dissipates — from your supply voltage, the LED's forward voltage and its current.

LED circuit

Supply voltage V

LED forward voltage V

Red ≈ 1.8–2.2 · green/yellow ≈ 2.0–2.4 · blue/white ≈ 3.0–3.4.

LED current mA

Typical indicator LED ≈ 20 mA — check the datasheet.

Results

Resistor value—

Nearest standard (E12)—

Resistor power—

Suggested resistor rating—

R = (Vsupply − Vforward) / I, power = (Vsupply − Vforward) × I. Pick a resistor rated at least 2× the calculated power. If supply ≤ forward voltage the LED won't light — raise the supply.