How to identify which replacement cartridge you need?
Look for Brand and Model number written on your system. Also, look for any filter models that can be written on each individual housing for systems that use more than one filter. You may be able to identify cartridges by system model. If you are unable to get any product numbers, remove each cartridge (or at least one) from its housing. For round cylinder filters, measure width and diameter, it should give an indication whether your filter is of standard size. For instance, a 10"x2.5" standard filter may measure 9 7/8" x 2 1/4" (and up to 3" in diameter). Standard sizes are 10x2.5, 20x2.5, 10x5 (10x4.5) and 20x5 (20x4.5) inches (first number is length, second diameter).