Whole-house cartridges are sold by nominal length (10 or 20 inches) and diameter class: “standard” or “slim” cartridges are about 2.5 inches across, and “Big Blue” cartridges are about 4.5 inches. The real dimensions differ by fractions of an inch. The Pentair “10-inch” cartridges in the table below run from 9.75 to 9.88 inches long, and its “2.5-inch” ones from 2.38 to 2.89 inches across. So a replacement fits when it matches your housing’s accepted diameter range, its length and its seal style, not just the label. Proprietary systems, such as quick-change heads, take the cartridge their maker names.
Disclosure: links to Amazon on this page are affiliate links. As an Amazon Associate, Better Water Guide earns from qualifying purchases.
What the size names mean, with real dimensions
These are the maximum dimensions Pentair publishes for its Pentek cartridges, a common reference brand for these formats.
| Nominal size | Common name | Example cartridges (diameter x length) | Pentair rating example |
|---|---|---|---|
| 2.5 x 10 in. | Standard or slim, 10-inch | Pentek P5 : 2.38 x 9.88 in.; Pentek EP-10 : 2.89 x 9.75 in. | EP-10: >6,000 gal chlorine at 1.0 gpm |
| 2.5 x 20 in. | Standard, 20-inch | Pentek P5-20 : 2.38 x 20 in.; Pentek EP-20 : 2.89 x 20 in. | EP-20: >12,000 gal at 2.0 gpm |
| 4.5 x 10 in. | Big Blue, 10-inch | Pentek DGD-5005 : 4.50 x 9.88 in.; Pentek EP-BB : 4.63 x 9.75 in. | EP-BB: >22,000 gal at 2.0 gpm |
| 4.5 x 20 in. | Big Blue, 20-inch | Pentek DGD-5005-20 : 4.50 x 20 in.; Pentek EP-20BB : 4.63 x 20 in. | EP-20BB: >44,000 gal at 4.0 gpm |
Dimensions are from Pentair’s P series , EP series and DGD series spec sheets. Chlorine capacities are Pentair’s internal test figures for chlorine taste and odor reduction.
10 vs 20 inch: what changes
Within one cartridge line, the longer and wider versions carry higher capacity and flow ratings. Pentair’s figures show the pattern:
- Carbon capacity rises with size. Pentair rates the EP-10 for more than 6,000 gallons of chlorine reduction at 1.0 gpm, the EP-20 for more than 12,000 gallons at 2.0 gpm, the EP-BB for more than 22,000 gallons at 2.0 gpm and the EP-20BB for more than 44,000 gallons at 4.0 gpm.
- Rated flow rises at the same pressure drop. Pentair lists the 10-inch DGD-5005 at under 1 psi initial pressure drop at 10 gpm and the 20-inch DGD-5005-20 at under 1 psi at 20 gpm.
- Housing pressure limits differ. Pentair’s Big Blue spec sheet rates its 10-inch housings to 100 psi and its 20-inch housings to 90 psi.
A bigger cartridge doesn’t change what the media does. A 20-inch sediment cartridge still doesn’t remove chlorine, and a Big Blue carbon block still doesn’t soften water. For sizing a new system rather than replacing a cartridge, use our housing size guide and flow-rate guide .
What each housing family accepts
Pentair publishes an accepted diameter range for each housing line, not one exact size. Its own lines show why “standard” isn’t a single dimension:
| Pentek housing line | Lengths | Ports | Accepts | Pressure and temperature |
|---|---|---|---|---|
| Traditional Standard | 10 and 20 in. | 3/4 in. NPT | 2-1/2 to 2-7/8 in. diameter cartridges | 125 psi; 40–125°F |
| 3G Standard | 10 and 20 in. | 3/4 in. NPT | 2-1/4 to 3-1/8 in. diameter; DOE or O-ring sealing | 125 psi; 40–125°F |
| Big Blue | 10 and 20 in. | 3/4, 1 or 1-1/2 in. NPT | Up to 4-1/2 in. diameter cartridges | 10 in.: 100 psi; 20 in.: 90 psi; 40–100°F |
Sources: Pentair’s Traditional Standard spec sheet , Big Blue spec sheet and Pentek full-line catalog . DOE means double open end.
Two details catch people out. First, seal style: Pentair says its 3G Standard housings accept both “standard double open end (DOE)” cartridges and its own O-ring sealing cartridges, so check which type your housing uses. Second, maximum dimensions can exceed the nominal class. Pentair lists the EP-BB’s maximum dimensions as 4.63 by 9.75 inches while describing its Big Blue housings as accepting “up to 4-1/2” diameter cartridges." When in doubt, follow the cartridge maker’s stated fit for your exact housing.
Replacements named by the makers
For packaged systems, the maker’s product page is the compatibility table that matters. These are the replacements each maker names.
| System or housing | Maker’s named replacement | What the maker says about fit |
|---|---|---|
| 3M Aqua-Pure AP902 (Amazon search) | AP910R (Amazon search) | Sanitary quick-change head |
| 3M Aqua-Pure AP903 (Amazon search) | AP917HD | Same AP900 quick-change head |
| 3M Aqua-Pure AP904 (Amazon search) | AP917HD-S (Amazon search) | Same AP900 quick-change head |
| iSpring WGB32B | FP25B sediment plus two FC25B carbon blocks | “fits standard 20” x 4.5” housings, including brand name models” |
| Pentair 20-inch Big Blue, such as 150233 (Amazon search) | Pentek DGD-5005-20 , among others | “can replace any 20” x 4.5" sediment filter" |
Sources: Solventum AP900 series page , iSpring’s FP25B and FC25B pages, and Pentair’s DGD-5005-20 page . AP902, AP903, AP904, AP910R, AP917HD-S and the 150233 housing have no in-stock Amazon listing sold by Amazon or the brand that we could verify, so those links are searches.
The AP900 heads are the clearest case of a proprietary format. Solventum’s “Sanitary Quick Change (SQC) style heads” take a cartridge that changes with a quarter turn, so buy the AP900 cartridge Solventum names rather than a standard 4.5 x 10 or 4.5 x 20 cartridge. A cartridge sold as compatible isn’t covered by the NSF listing below, which names the maker’s own cartridge.
Certification: what a replacement’s listing covers
A certification listing belongs to a specific cartridge or cartridge-and-system pair. It doesn’t transfer to a look-alike.
- System claims. NSF’s listing for Solventum pairs the AP903 with the AP917HD element and the AP904 with the AP917HD-S, each under NSF/ANSI 42 for chlorine, taste and odor, and Class III nominal particulate reduction.
- Material-only listings. Pentair says the P5, P5-20, EP series and DGD series cartridges are “Tested and Certified by NSF International to NSF/ANSI Standard 42 for material requirements only.” That covers what the cartridge is made of, not how much it removes.
- Tested, not listed. iSpring says the FP25B and FC25B are “tested by an independent third-party to meet NSF/ANSI standards.” NSF’s listing for iSpring shows only reverse osmosis systems.
Our certification guide explains how to check a listing for the exact cartridge.
How to find the right replacement
- Read the housing cap or old cartridge. A part number such as 150233 or AP904 tells you the format faster than a tape measure.
- Measure the old cartridge if there’s no part number. Measure diameter and length, and compare them with the housing maker’s accepted range rather than the nominal 10 or 20.
- Check the seal style. Find out whether your housing takes double open end (DOE) cartridges, O-ring sealing cartridges, or, like Pentair’s 3G Standard line, both.
- Match the media to the job. Replace sediment with sediment and carbon with carbon at the micron rating your system was designed around. Our rust and sediment list covers when to go coarser or finer.
- Follow the system maker’s change interval. iSpring lists its WGB32B replacement pack at every 6 to 12 months. A rising pressure drop is also a sign it’s time. See our pressure-drop guide .
If you’re choosing a complete system instead, see our best whole-house water filters , and compare the two formats in Big Blue vs slim .
Sources
- Pentair Pentek P series spec sheet (P5 and P5-20 dimensions, NSF material listing)
- Pentair Pentek EP series spec sheet (EP-10, EP-20, EP-BB, EP-20BB dimensions and chlorine capacity, NSF material listing)
- Pentair Pentek DGD series spec sheet (DGD-5005 and DGD-5005-20 dimensions and pressure drop)
- Pentair Pentek Big Blue housing spec sheet (lengths, ports, accepted diameter, pressure and temperature)
- Pentair Pentek Traditional Standard housing spec sheet (lengths, ports, accepted diameter)
- Pentair Pentek full-line catalog (Traditional Standard ratings, 3G Standard diameter range and seal styles)
- Pentair DGD-5005-20 product page (fit statement)
- Solventum 3M Aqua-Pure AP900 series page (AP902, AP903, AP904 replacement cartridges, quick-change head)
- iSpring FP25B product page and FC25B product page (fit statements, testing claim)
- iSpring WGB32B product page (replacement interval)
- NSF listing for Solventum and NSF listing for iSpring (certification scope)
Dimensions, fit statements and listings were checked on October 5, 2026. This is desk research from maker documents; Better Water Guide has not tested these cartridges.