How to Measure Spa Filters

Measuring a hot tub filter is easy.

Measure the length, then the width or outer diameter.

Finally measure the diameter of the inner hole if there is one, or note the features of the top and bottom of the filter. Does it have a top handle or a threaded bottom? If there are threads on bottom, are the threads fine (mpt) or course (sae)?

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Filter Model Number - Enter into Search Box Above
If you have a filter model number, you can just search by model. It is always a good idea to measure your existing filter to be sure you get the correct replacement filter.

One of the biggest problems that come up when ordering a replacement filter with bottom threads is getting the thread type and size right. Most filters with threads have either fine threads (mpt) or course threads and they can be male or female type threads.

There are two main types of threads on the bottom of spa filters.

A course thread (or SAE thread) and a fine thread (or MPT thread). The course thread only has a few, larger spirals while the fine thread has many more thinner and closer together spirals.

Thread measurements are nominal and relate to plumbing size, not measurement of the threads.

Popular Hot Tub Filter Thread Measurements

1 1/2 inch mpt fine threads correspond to a measured outer diameter across threads of 1 7/.8"
2 inch mpt fine threads correspond to a measured outer diameter across threads of 2 5/16"
1 1/2 inch course threads correspond to a measured outer diameter across threads of 1 13/16"
2 inch course threads correspond to a measured outer diameter across threads of 2 3/8"

For the female threaded connection a nominal measurement of 1 1/2 inch Female SAE or course threads corresponds to an inner diameter measurement of about 1 7/8"

Search by filter part number in the search box at the top of the page, or let us do the work for you.