LED Series Resistor Calculator

Electricity
17 calculations
Having trouble? Go to tutorial
📝 How it works:
Calculate the series resistor for LEDs from supply voltage, LED forward voltage and LED current. With E12 standard value, power dissipation and series/parallel wiring.

Fill in the fields below and click "Calculate".
e.g. 5 V (USB), 12 V, 3.3 V
red ≈ 1.8–2.2 V, blue/white ≈ 3.0–3.4 V
standard LED usually 20 mA

The series resistor limits the current through an LED: R = (Uq − ULED) / ILED. It absorbs the difference between the supply and LED forward voltage. The calculator returns the next E12 standard value and the required power rating (P = I²·R) – for series and parallel wiring of several LEDs.

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