How to Measure Your Pool or Spa Filter Cartridge
If you’re trying to find the correct replacement filter cartridge for your pool or spa, the most reliable method is to measure your existing cartridge dimensions. This guide walks you through the exact measurements you need—height, outside diameter, and top/bottom openings so you can find the right replacement filter even if the model number or label is no longer visible.
Knowing your filter dimensions helps you identify the right replacement, improve system performance, and avoid costly returns.
How to Measure Your Pool or Spa Filter Cartridge Dimensions (Step-by-Step Guide)
Step 1: Measure the Outside Diameter
Place your cartridge upright on a flat surface. Using a tape measure, determine the outside diameter of the end cap.
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Measure across the widest point
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Use exact measurement (± 1/16")
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Common diameters: 4.5"–10"
This is one of the most important dimensions when identifying your replacement.
Step 2: Measure the Cartridge Length
Measure the total length of the cartridge from end cap to end cap.
Important:
Do not include handles, standpipes, threaded ends, or extensions. Measure only the flat plastic end caps.
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Use exact measurement (± 1/16")
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Typical length: 9.75"–33"
Step 3: Measure the Top Inside Diameter
If your cartridge has an open top, measure the inside diameter of the opening.
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Measure the narrow opening edge-to-edge
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Use exact measurement (± 1/16")
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Skip this step if the top is closed, threaded, or handled, but take note of the end cap type.
This measurement helps match your filter to the correct replacement series.
Step 4: Measure the Bottom Inside Diameter
If your cartridge has a bottom opening, measure the inside diameter of the opening.
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Measure the narrow opening edge-to-edge
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Use exact measurement (± 1/16")
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Skip this step if the bottom is closed, threaded, or handled, but take note of the end cap type.
Ready to Find Your Replacement Filter?
Use our filter replacement finder to search for the right filter using these dimensions, or search by part number or manufacturer.
Why Measuring Your Filter Cartridge Is Important
Pool and spa cartridges often look similar, even when they fit completely different systems. Measuring your filter directly is the most reliable way to find a replacement—especially if the OEM label has faded or the model number is no longer visible on your housing.
Correct measurements ensure:
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A proper seal inside the filter housing
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Better filtration performance
- Prevents water bypass
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Lower pump strain
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Longer cartridge life