Whole House Water Filter Cartridge Sizes & Types — Which One Do You Need?

Q: What's the difference between a 10-inch and 20-inch whole house filter?

Length and capacity. A 20-inch Big Blue cartridge holds roughly twice the filtration media of a 10-inch cartridge, so it lasts longer between changes and handles higher water usage before clogging. Diameter is the same 4.5 inches on both.

Q: Can I mix sediment and carbon cartridges in a dual-stage system?

Yes, that is how most dual-stage systems are designed to work. Install the sediment cartridge in the first housing closest to your water supply, and the carbon cartridge in the second, so sediment does not clog the carbon media prematurely.

Whole house filter housings almost always take one of two standard cartridge lengths, but the media inside — sediment, carbon, or both — is a separate choice that trips up just as many people. Get either one wrong and you’ll either buy a cartridge that doesn’t fit your housing, or one that fits fine but doesn’t filter the thing you actually needed filtered. This guide covers both: how to identify your cartridge size, and how to pick the right media type.

Already know your housing brand? Check our GE, Culligan & American Plumber compatibility guide → for a verified match instead of guessing from the chart below.

How to Tell Your Cartridge Size

Whole house cartridges are sold by two measurements: length and diameter. Diameter is almost always 4.5 inches for standard residential systems — length is where the real split happens. Measure your existing cartridge (or the empty housing) end to end. A cartridge around 9.75 inches is a “10-inch” nominal system; one around 19.75 inches is a “20-inch” nominal system, sometimes labeled “Big Blue.” The nominal number is always rounded up slightly from the actual measurement, same as HVAC filter sizing.

Whole House Filter Cartridge Size Chart

Nominal Size	Actual Length	Common Housing Brands	Find a Match
10″ x 4.5″	~9.75″ x 4.5″	GE GXWH40L/GXWH35F, Culligan RFC-BBSA, American Plumber W10-PR/W10-BC/WRC25HD	Check verified match →
20″ x 4.5″ (“Big Blue”)	~19.75″ x 4.5″	High-capacity and well-water systems, larger households	Not yet in our verified tool

If your cartridge doesn’t match either length, measure it directly rather than assuming — a handful of systems use non-standard housings, and a cartridge that’s even half an inch off either won’t seat properly or will leave a gap that lets unfiltered water bypass the media entirely.

Sediment vs. Carbon vs. Carbon+KDF: Which Media Do You Need?

Sediment-only — a pleated or spun polypropylene cartridge that removes dirt, rust, and sand. It does nothing for chlorine taste or odor. Use it as a first-stage filter ahead of a carbon cartridge, or on its own if particulate is your only issue (common on well water).
Carbon block — removes chlorine taste and odor plus some chemicals, but doesn’t handle heavy sediment well since it clogs faster with particulate load. This is the standard choice for municipal (city) water, which is usually already low in sediment.
Carbon + KDF — adds heavy metal reduction (lead, mercury) and bacteriostatic properties on top of standard carbon block’s taste/odor removal. Costs more, worth it if your water report flags heavy metals.

Many whole house systems run two housings in sequence — a sediment pre-filter followed by a carbon or carbon+KDF cartridge — rather than trying to do both jobs with one cartridge. If your system only has a single housing, match the media to your actual water quality issue rather than defaulting to whichever cartridge is cheapest.

How Often to Replace Your Whole House Filter

Carbon and carbon+KDF cartridges typically last 3 to 6 months for average residential use. Sediment cartridges vary more — every 1 to 3 months on well water with heavy particulate, up to 6 months on cleaner municipal water. Watch for two signs regardless of the schedule: dropping water pressure (the cartridge is clogged with sediment) or the return of chlorine taste or odor (the carbon is exhausted, even if the cartridge still looks fine).

Find Your Verified Match

Know your housing brand? Our GE, Culligan & American Plumber whole house guide cross-references manufacturer specs and retailer data for a confirmed replacement — not just a similar-looking part number.

Frequently Asked Questions

What’s the difference between a 10-inch and 20-inch whole house filter?
Length and capacity. A 20-inch (“Big Blue”) cartridge holds roughly twice the filtration media of a 10-inch cartridge, so it lasts longer between changes and handles higher water usage before clogging — common on larger households or well-water systems with heavier sediment loads. Diameter is the same 4.5 inches on both.

Do I need a sediment filter, a carbon filter, or both?
If your water has visible dirt, rust, or cloudiness, you need a sediment stage. If it has chlorine taste or odor, you need a carbon stage. Many homes need both, run as two separate housings in sequence rather than one cartridge trying to do both jobs.

How do I know what size cartridge my housing takes?
Measure your existing cartridge end to end, or check the housing itself for a stamped model number. Round the measurement up to the nearest standard size (10″ or 20″) — that’s the nominal size you order.

Can I mix sediment and carbon cartridges in a dual-stage system?
Yes — that’s how most dual-stage systems are designed to work. Install the sediment cartridge in the first housing (closest to your water supply) and the carbon cartridge in the second, so sediment doesn’t clog the carbon media prematurely.

Other Filter Tools

Also need a filter match for something else?

Every match on this page is cross-referenced against manufacturer specs and retailer data — not just similar-looking part numbers. How we verify compatibility →