LED Resitor Calculator

I have a bunch of LEDs that I want to power using some fixed input voltage. How many LEDs can I put in series, and how big of a resistor should I put in series with them all?

If you want multiple LEDs of the same type in parallel, add the number of parallel 'columns' you want under 'columns'. The total number of LEDs will be rows * columns, and the recommended resistance is for a single resistor in series with everything (see diagram at bottom of page).

If you want to put multiple LEDs of different voltages in series, add their voltages up and enter the bunch as one LED.

Label LED LED voltage Power supply voltage Recommended Efficiency
current columns min max min max LED rows resistance low-V high-V

Disclaimer: These calculations assume the LEDs draw a constant current, but I'm actually not sure how typical LEDs behave under high or low voltage conditions.

It's assumed that your circuit is set up like the following, if you chose 2 columns and have enough voltage for 3 rows:

Two parallel columns of 3 LEDs in series, with a resistor and a power supply in series with everything