💡 LED Resistor Calculator
Enter your supply voltage, LED forward voltage, and desired current to find the right series resistor for your circuit.
What This Calculator Does
LEDs need a current-limiting resistor in series to keep them from drawing too much current and burning out. This calculator finds the resistor value and power rating needed for a given supply voltage, LED forward voltage, number of LEDs wired in series, and target operating current.
The Formula
Using Ohm’s law, the resistor value is R = (Vsupply − n × VLED) ÷ I, where n is the number of LEDs in series and I is the desired current in amps. The resistor’s power dissipation is P = I² × R, which tells you what wattage resistor to buy — always choose a resistor rated comfortably above the calculated dissipation.
- Forward voltage varies by LED color and type (roughly 1.8–2.2V for red, 3–3.4V for blue/white); check your LED’s datasheet for the exact value.
- Typical currents are 10–20mA for standard indicator LEDs and higher for high-power LEDs — check the datasheet’s maximum rating.
This calculator is for general electronics planning and educational purposes; always confirm your LED’s actual forward voltage and maximum current rating before building a circuit.