There are 4 common sizes for sediment filters. For under sink applications - a 2-1/2” X 10” size is most common. For whole house and well water applications - a larger 4-1/2” X 10” format is common - and sometimes referred to as “Big Blue”. 4-1/2” X 20” filters are also used in residential whole house and commercial application. 2-1/2” X 20” filters are most used in commercial food and beverage applications.