LED Resistor Calculator

Use this LED resistor calculator to find the resistor you need in series with your LED, so that the LED gets the right amount of current.

An LED “grabs” the voltage it needs, its forward voltage, and the rest of the supply voltage drops across the resistor. So you can find the resistor value with Ohm’s law:

$$R=\frac{V_{SUPPLY}-V_{LED}}{I_{LED}}$$

Fill in your supply voltage, the LED color (or its forward voltage from the datasheet) and the current you want. If you’re not sure about the current, somewhere between 1 mA and 10 mA is usually plenty for a standard LED:

How to Use the Result

You probably won’t find a resistor with the exact value, so the calculator also gives you the nearest standard value that is higher. A slightly higher resistance gives a little less current, which is safe for the LED.

The power rating is the power the resistor turns into heat, times two for some margin. Most small resistors are rated for 1/4 W, which is more than enough for a typical LED.

With several LEDs in series, add up their forward voltages. The supply voltage has to be higher than the total, or the LEDs won’t light up.

Want to learn more? Check out how to find the voltage and current of an LED, or read more about the current limiting resistor.