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LED Resistor Calculator

Every LED needs a current-limiting resistor. Enter your supply voltage and LED parameters to get the exact series resistor, the nearest standard value, and the required power rating.

Circuit Parameters

How It Works

The resistor drops the difference between the supply voltage and the LED forward voltage at the desired current:

R = (Vsupply − n × Vforward) ÷ I

Since exact values are rarely manufactured, the calculator suggests the nearest standard resistor from the E12 and E24 series, rounding up so the LED current stays at or below your target. The power dissipated in the resistor is P = I²R; choose a resistor rated for at least twice that for a comfortable margin.

Typical indicator LEDs run at 10–20 mA. Modern high-brightness LEDs are often clearly visible at 2–5 mA, which extends battery life.

Related Utils

Ohm's Law Resistor Color Voltage Divider SMD Resistor Code

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