LED Current-Limiting Resistor Calculator

Show/Hide: Definitions Formulae Instructions

Introduction:

The calculator on this page allows you to detemine the correct size/value/resistance of current-limiting resistor required to run an LED at the right current for that type.
(The datasheet for your chosen LED will specify a max-current, but you should always design your circuit for a slightly lower current for safety, and to prevent premature burn-out of the component.) This calculator will also work for two or more LED's in series, if you first add up the voltage drop required for each LED.
Click on any of the links at the top of the page to reveal (or hide) more information about this calculator.

Caveats:

If you are reading this paragraph, then you probably don't have JavaScript installed/enabled.
At this point in time the calculators on this site are entirely dependent on JavaScript. Given enough time and money it is hoped to develop a version in the future which will be able to operate independently. Since JavaScript runs on your own computer, rather than on this server, it has been possible to set up this site much more quickly than if a server-side language was used, and it is possible to serve far more pages with the available bandwidth.
If you think that you can assist with this project in any way, then please visit the Support section and leave a message.

Definitions:

V_t: Total Voltage drop across the LED and resistor
V_LED: Voltage drop rating, across the LED or LEDs in series
I: Current rating of the LED / current through the finished system
R: Value of Resistor required to limit the current

Formulae:

V = I * R
R = (V_t - V_LED) / I

Instructions

Enter a value into each text-box in the form below.
Choose appropriate unit-sizes for each value from each drop-down list.
Hit the ENTER or RETURN key on your keyboard, or press the 'CalcResult' button below the input fields.
A results area will appear at the bottom of the page, showing the required resistance value.
Press the 'Clear Results' button if you wish to discard the current results list, otherwise further calculations will be added to the bottom of the current results list.