LED Resistor Calculator
Work out the resistor needed to safely power an LED from your supply voltage.
Protecting an LED
An LED will destroy itself if connected directly to a supply, because it draws as much current as it can and burns out. A series resistor limits that current to a safe level. This works out the right resistor value from your supply voltage and the LED's characteristics, the essential calculation for any LED circuit.
Enter the supply voltage and LED details to get the resistor value.
Why the resistor is not optional
The mistake beginners make is wiring an LED straight to a battery and watching it flare and die, because an LED has very little resistance of its own and nothing to limit the current. The resistor takes up the difference between your supply voltage and the LED's own voltage drop, setting the current to the level the LED is rated for. Choosing a value a little higher is safe — the LED is slightly dimmer but protected — while too low risks its life.
Common questions
Why does an LED need a resistor?
Because an LED has little resistance of its own and will draw too much current and burn out if connected directly. The resistor limits the current.
What if I use a slightly larger resistor than calculated?
The LED is a little dimmer but safely protected. Too small a resistor is the dangerous direction, risking the LED's life.
Is anything uploaded?
No. The calculation happens in your browser.