Here is an excellent resource, certainly worth bookmarking if you are creating your own LED lighting systems – the LED series/parallel array wizard.
It describes itself:
The LED series/parallel array wizard is a calculator that will help you design large arrays of LEDs. The LED calculator was great for single LEDs–but when you have several, the wizard will help you arrange them in a series or combined series/parallel configuration. The wizard determines the current limiting resistor value for each portion of the array and calculates power consumed. All you need to know are the specs of your LEDs and how many you’d like to use.
Check out the screen grab below for our example generation.