How to Measure Hot Tub Filters

Measuring your filter cartridge may not be as straight forward as it at first seems.

hot tub filters width Please read the notes below to be sure that you get the correct measurements.

Remember that all measurements may vary by about 1/8" due to expansion/shrinkage of the cartridge over time.

Measure the outside diameter (width) of the filter cartridge (in inches or centimetres), that is the maximum distance from one side to the other.

Measure the length of the filter cartridge from end cap to end cap. Include the thickness of the caps but do not include handles or screw threads in the measurement.

Identify the end cap configuration. Is it threaded, with a handle, or open on both sides?

If it is open, measure the inner diameter of the hole, excluding any taper.

If it has a male thread, identify which type of thread it is. There are only two types of thread:

Regular threads are fine, tightly spaced, with relatively sharp edges. Fine threaded filters are listed in 2 nominal sizes: either 1 1/2" or 2" MPT (male pipe thread). [Please note that a 1 1/2" MPT actually measures 1 3/4" outside diameter and a 2" MPT thread measures 2 1/4" outside diameter!]

The SAE type is a very coarse, widely spaced, flat-edge thread. Since there are only a few SAE threaded filter types, it is only necessary to verify the SAE threaded filter's other dimensions and style to confirm that you have a perfect match.

Some Pleatco brand filters have a removable male pipe thread fitting which slip-fits into a 1.9" hole in the filter bottom. You may need to unscrew the male pipe fitting from your spa's filter housing if it did not come out with the old filter (many hot tub owners are not even aware that the fitting is still in there). Most other brand filters are molded as a single piece, so that the threaded fitting comes off with the filter
Filters with smooth (non-threaded) male slip fittings come in only 2 nominal slip fitting sizes: 1 3/4" which is the actual outside diameter, or 2" which measures approx. 2 1/4" outside diameter!
After all that, if you are still having trouble identifying the correct filter, count the number of pleats! It might take a while but the pleat count determines the filtration area of the filter and so enables you to distinguish between filters with the same dimensions. When you view the detailed information about each filter the pleat count is usually given.