Enter all 3 values and click 'Calculate'

Source Voltage
(Volts):

LED Forward Voltage
(Volts):

LED Forward Current
(Milliamps):

Using the correct resistor with an LED is important. Too little resistance and the LED will blow, and too musch makes the LED dim. To calculate the correct resistance needed, simply take the voltage drop of the LED away from the source voltage, and then apply Ohm's law as you would normally to calculate resistance:

R = (Vs x Vled) / I

R is the resistance in ohms, Vs is the source voltage, Vled is the the voltage drop of the LED, and is the current through the LED in milliamps.

It's important to use the correct resistor but it can be a bit laborious calculating the values by hand. Our online LED resistor calculator makes it easy for you. Simply enter the 3 values, hit calculate, and the correct resistor value will be shown!

You may notice that the actual value of the formula differens to the resistor value shown. This is because resistors only come in a few specific values. Our calculator rounds the value up to the nearest common resistor value, showing you a value that you will be easily able to find.