How to measure your hot tub filter

How to measure your hot tub filter

There are literally hundreds of different hot tub filters out there. Finding the correct replacement filter can be tricky as the numbers on the filter don't always help you find the correct one.

The best method is finding the correct replacement filter is by measuring your existing filter, sending us those measurements and we'll do whatever we can to find and stock the correct filter.

Here's a guide on how to measure your hot tub filter.

Diameter (width)

filter-width.jpgStart by measuring the diameter of your hot tub filter across the outside edges of the end cap (usually blue in colour) at its widest point as displayed.

Note: measurements can vary by about 1/8" due to the old filter shrinking, expanding or manufacturers variances. For example, if you measure a diameter of 5" and can't find a match, the correct measurement of the replacement filter may be 4-15/16".



filter-length.jpgNext measure the length of the filter from end cap to end cap (outside of the endcap to the outside of the end cap). If your filter has a handle on the top or fitting on the bottom, do not include this in your measurement.

Note: as mentioned above, measurements may vary by about 1/8" due to shrinkage, expanding or manufacturers variances.


Opening Diameter (Top/Bottom Hole diameter)

filter-inner.jpgYour filter may have an opening on one end or on both ends. Measure the hole diameter (width) as shown in the image. If your filter has a slotted hole, do not include the slot in the measurement. Measure the narrowest point.

Note: some closed top filters have a small pin-hole which allows trapped air to escape when installing. This would not be considered a top hole filter and does not need to be measured.


Thread Types/Sizes

Some hot tub filters have threads at the bottom; either male or female threads. You will need to determine the type of thread your filter has:

  • MPT - which are fine threads
  • SAE - which are course threads


After identifying the thread type, you will need to determine the size. For Fin threads (MPT) they are usually 1-1/2" or 2". For course threads (SAE) they are 1-1/4" or 1-1/2" or 2"

Note: The actual outside diameter of the thread type is different than the measurement noted. MPT threads actual outside diameter is 1/4" larger. For example, a 1-1/2" MPT threads outside diameter actually measure 1-7/8" . SAE threads actual outside diameter is 5/16" larger. For an example, a 2" SAE thread measures 2-5/16".

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