LED Resistor Calculator

Enter value and click on calculate. Result will be displayed.
Source Voltage:
Volts
Forward LED voltage:
Volts
LED Current:
miliAmps
Resistor:
Ohms

An LED Resistor Calculator is a tool that helps you determine the right resistor value needed when connecting an LED (Light Emitting Diode) to a power supply. LEDs require a specific amount of current to operate safely — too much current can burn them out, and too little can make them dim or not light up at all.

The resistor in the circuit controls the current flowing through the LED, and the calculator uses Ohm's law to figure out the correct resistor value.

The formula it uses is:


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Where:
R = Resistor value (in ohms Ω)
Vs = Supply voltage (in volts V)
Vf = LED forward voltage (in volts V) — the voltage drop across the LED, often 1.8V to 3.3V depending on LED color/type
I = LED current (in amperes A) — typical LEDs run at 10mA to 20mA (0.01A to 0.02A)
For example:
If you have a 9V supply, a red LED with a 2V forward voltage, and 20mA of desired current:

So you'd need a 350-ohm resistor (or the nearest standard value like 330Ω or 360Ω).