Compare LED strip size and number of LEDs on the strip
Traditionally, LED strip lights are packaged on a reel (spool) of 5 meters, or 16' 5''. The machines used to "pick and place" the LEDs and resistors on the flexible circuit board are typically 3' 2'' in length, so individual sections are soldered together to complete a whole reel. If purchasing, make sure you are purchasing by the foot or by the reel. Confirm length before checking out.
Measure how many feet you need of LED strips before you start. This will make it easier to compare price (after quality is compared, of course). Once you determine the number of feet on the reel being sold, look at how many LED chips are on the reel and the LED chip type. This can be used to compare LED strips between companies.