Free calculator
Whole House Water Filter Size Calculator
Enter your bathrooms, household and water source, then what you want out of the water. Get the peak flow, port size, cartridge size and filter type you need, how often you will change cartridges, and systems that fit.
Updated Oct 24, 2026
- Answer a few questions
- See the math behind every number
- Get models that actually fit
Every whole house filter this tool can recommend
Sorted by price. Flow ratings, cartridge sizes and what each one reduces come from the maker's listing.
iSpring WGB21B 2-Stage Whole House Filter (10 in.)
- 10 x 4.5 in. filters
- 1 in. ports
- 50,000 gal per set
- 5 micron sediment
Two 10 x 4.5 in. Big Blue housings: a 5 micron sediment filter, then a coconut shell CTO carbon block for chlorine, taste and odor. 1 in. ports, pre-mounted on a bracket.
- Reduces over 90% of chlorine plus taste, odor and VOCs
- 1 in. inlet and outlet, pre-assembled on the bracket
- Filter wrench and pressure release valve included
- 10 in. cartridges: 50,000 gallon set, changed every 3 to 6 months
- Does not treat chloramine, lead, iron or hardness
$100 to $250, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
iSpring WGB21B-PB Lead and Chloramine Whole House Filter (10 in.)
- Lead + chloramine
- 10 x 4.5 in. filters
- 1 in. ports
- Up to 15 GPM
A CTO carbon block, then iSpring's FCRC15B lead filter, rated to take lead from 100 ppb down to the 15 ppb EPA action level. iSpring sells it as a lead and chloramine system.
- Lead filter rated from 100 ppb down to 15 ppb or less
- Up to 15 GPM through 1 in. ports
- Standard 10 x 4.5 in. cartridges
- No separate sediment stage; the carbon block is the first stage
- 50,000 gallon carbon stage, changed about every 6 months
$100 to $250, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
iSpring WGB22B 2-Stage Whole House Filter (20 in.)
- 20 x 4.5 in. filters
- 1 in. ports
- 100,000 gal per set
- Up to 15 GPM
Two 20 x 4.5 in. Big Blue housings: 5 micron sediment, then a CTO carbon block that reduces up to 99% of chlorine. Twice the cartridge length of the 10 in. systems, rated 100,000 gallons per set.
- Reduces up to 99% of chlorine, taste and odor
- 100,000 gallons per set, about a year for a family of four
- Industry-standard 20 x 4.5 in. cartridges, 1 in. FNPT
- One carbon stage; the 3-stage WGB32B adds a second
- Does not treat chloramine, lead, iron or hardness
$250 to $500, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
iSpring WGB21B-PFKS PFAS and Heavy Metals Whole House Filter (10 in.)
- PFAS + chloramine
- Lead, mercury, H2S
- 10 x 4.5 in. filters
- 1 in. ports
Stage 1 is KDF plus granular carbon for chlorine, chloramine, lead, mercury and hydrogen sulfide; stage 2 is a carbon block SGS-tested to reduce up to 99% of PFAS (PFOA and PFOS).
- SGS-tested to reduce up to 99% of PFAS
- Also reduces chloramine, lead, mercury and hydrogen sulfide
- City or well water, 1 in. NPT ports
- Compact 10 in. filters, sold for smaller homes
- 50,000 gallons or 12 months per filter set
About $359.99 at iSpring, checked Oct 24, 2026
Check price at iSpringPaid link. We earn a commission at no cost to you.
Show all 12 modelsShow fewer
Home Master HMF2SmgCC Whole House Filter (Catalytic Carbon)
- 10 GPM
- Chloramine + chlorine
- 25 to 1 micron sediment
- 1 in. ports
A 4-layer 25 to 1 micron sediment filter, then up-flow KDF85 catalytic carbon that Home Master rates for chloramines and chlorine, 95,000 gallons per carbon filter.
- Catalytic carbon rated for chloramines as well as chlorine
- 95,000 gallon carbon filter, about a year for a family of four
- 1 in. NPT ports, steel bracket fits 16 in. studs
- Rated 10 GPM, less than 15 GPM systems
- Replacement set is Home Master specific
$250 to $500, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
iSpring WGB32B 3-Stage Whole House Filter (20 in.)
- 20 x 4.5 in. filters
- 1 in. ports
- 100,000 gal per set
- Up to 15 GPM
Three 20 x 4.5 in. housings: 5 micron sediment, then two CTO carbon blocks in a row for chlorine, taste, odor and VOCs. Up to 15 GPM through 1 in. ports.
- Two carbon stages, up to 99% chlorine reduction
- Up to 15 GPM through 1 in. NPT ports
- 100,000 gallons per set, about a year for a family of four
- Does not treat chloramine, lead, iron or hardness
- Three housings need more wall space than a 2-stage
$250 to $500, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
iSpring WGB32B-PB Lead-Reducing Whole House Filter (20 in.)
- Lead + chlorine
- 20 x 4.5 in. filters
- 1 in. ports
- Up to 15 GPM
5 micron sediment, a CTO carbon block, then the FCRC25B lead filter rated for 150,000 gallons at 100 ppb lead. Full size 20 in. cartridges for larger homes.
- Lead stage rated 150,000 gallons at 100 ppb
- Up to 15 GPM through 1 in. NPT ports
- Sediment and carbon stages rated 100,000 gallons
- iSpring does not list chloramine for this model
- Three 20 in. housings need wall space
$250 to $500, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
iSpring WGB32BM Iron and Manganese Whole House Filter (20 in.)
- Iron + manganese
- 20 x 4.5 in. filters
- 1 in. ports
- Up to 15 GPM
Sediment, a carbon block, then the FM25B catalytic iron filter rated for up to 3.0 ppm iron and 1.0 ppm manganese. Built for wells with mild iron staining.
- Iron up to 3.0 ppm and manganese up to 1.0 ppm
- Also reduces sediment, chlorine, taste and odor
- Up to 15 GPM, 1 in. NPT ports
- Over 3 ppm iron needs an air-injection iron filter
- Does not soften hard water
$250 to $500, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
Express Water Heavy Metal 3-Stage Whole House Filter
- 15 GPM
- Heavy metals
- Pressure gauges
- 1 in. connection
+1 moreFewer
- Stainless bracket
Sediment, a KDF heavy metal stage and a carbon block on a stainless steel bracket and free-standing frame, with a pressure gauge and pressure release button on each housing.
- KDF stage reduces lead, nickel, chromium and other heavy metals
- Pressure gauges show when a filter is clogging
- Stainless steel bracket and free-standing frame
- Filters every 6 to 12 months or 100,000 gallons
- Does not soften; goes ahead of a softener if you have one
$250 to $500, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
Home Master HMF3SdgFeC Well Water Whole House Filter (Iron)
- Well water
- Iron + sulfur
- 20 x 4.5 in. filters
- Up to 15 GPM
Fine sediment, a radial flow iron filter and radial flow carbon in 20 x 4.5 in. housings. Home Master builds it for well water: up to 95% of iron, manganese and sediment, up to 3 ppm combined load.
- Iron, manganese and hydrogen sulfide, up to 3 ppm combined
- Up to 15 GPM through 1 in. ports
- 4-layer 25 to 1 micron sediment filter
- Home Master sends city water users to the HMF2SmgCC
- Maker does not publish a gallon rating for the filter set
$500 to $1,000, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
iSpring WGB32B-KSNC Chloramine and Heavy Metals Whole House Filter (20 in.)
- Chloramine + lead
- Catalytic carbon
- 20 x 4.5 in. filters
- Up to 15 GPM
Sediment, a KDF plus carbon stage for lead, mercury and hydrogen sulfide, then a catalytic carbon block SGS-tested to remove up to 94.4% of chloramine. For cities that disinfect with chloramine.
- Catalytic carbon: up to 94.4% chloramine removal (SGS)
- Also reduces lead, mercury, hydrogen sulfide and chlorine
- Up to 15 GPM through 1 in. NPT ports
- Replacement set is sold by iSpring direct
- 100,000 gallons or 12 months per set
About $639.99 at iSpring, checked Oct 24, 2026
Check price at iSpringPaid link. We earn a commission at no cost to you.
Aquasana Rhino EQ-1000 Whole House Filter (1,000,000 gal)
- 14.6 GPM
- Carbon + KDF tank
- 10-year media
- 3/4 or 1 in. fittings
A carbon and KDF tank rated for 1,000,000 gallons or 10 years, with a 20 in. sediment pre-filter and a post-filter. Reduces 97% of chlorine at 14.6 GPM.
- Tank media rated 1,000,000 gallons or 10 years
- 14.6 GPM with no noticeable pressure change, per Aquasana
- Install kit with brass fittings for 1 in. or 3/4 in. pipe
- Pre-filter and post-filter changes every 2 months
- Chlorine model; Aquasana does not list chloramine for it
$1,000 to $2,000, live price on Amazon
Check price on AmazonPaid link. We earn a commission at no cost to you.
Some of these links pay us a commission and some do not; each card says which. Commissions do not affect which models the tool picks or how it ranks them. See our disclosure.
How this calculator works
- Peak flow. One shower per bathroom (capped at the number of people) at 2.5 GPM, the federal showerhead maximum, plus two fixtures at 2.2 GPM, the federal faucet maximum (10 CFR 430.32), all running at once. That gives about 7 GPM for 1 bathroom and 12 GPM for 3, in line with water treatment sizing tables. The plumbing code's fixture unit method (IPC Appendix E) gives higher numbers because it sizes pipes for worst-case demand.
- Ports. At 8 ft/s, the Copper Development Association's cold water velocity limit, a 3/4 inch type L copper line carries about 12 GPM and a 1 inch line about 20. Over 12 GPM, or on a 1 inch main, we call for 1 inch ports.
- Cartridge size. Up to 10 GPM, 10 x 4.5 inch cartridges are enough; above it we pick 20 x 4.5 inch cartridges or a tank. Where the maker publishes a flow rating, it must meet your peak.
- Media. City water needs carbon for chlorine, or catalytic carbon when the utility uses chloramine. Wells need a sediment stage. Lead, PFAS, iron and hydrogen sulfide each need a system whose maker lists that contaminant. Over 3 ppm iron goes to an air-injection iron filter, since cartridge iron filters are rated to 3 ppm. Hardness goes to a softener.
- Cartridge life. 70 gallons per person per day, between the Water Research Foundation's REU2016 indoor figure (about 59) and EPA WaterSense's 82 gallons at home, since a whole house filter also sees outdoor taps plumbed after it. Months between changes = rated gallons / monthly use, capped at the maker's month limit. Yearly cost uses each replacement set's listed price.
- Ranking. Systems that pass are ranked by five-year cost: price plus five years of replacement sets. Cards run Budget, Best fit, Premium by actual price.
Worked examples
2 bathrooms, 4 people, chlorinated city water
- 2 bathrooms, 4 people, 3/4 inch main
- City water, chlorine
- Chlorine taste and smell
9.4 GPM peak. A 2-stage 10 inch sediment and carbon system; cartridges every 6 months.
Two 2.5 GPM showers plus two 2.2 GPM faucets is 9.4 GPM, inside what 10 x 4.5 inch cartridges handle. Four people use about 280 gallons a day, 8,500 a month, so a 50,000 gallon set lasts just under 6 months, which is also iSpring's change interval. A 20 inch system costs more up front but goes about 12 months between changes.
3 bathrooms, 5 people, chloramine city water, older pipes
- 3 bathrooms, 5 people, 1 inch main
- City water, chloramine
- Taste and lead
11.9 GPM peak. A 3-stage 20 inch system with catalytic carbon and a lead stage, 1 inch ports.
Three showers and two faucets is 11.9 GPM, over the 10 GPM where we move to 20 inch cartridges. Ordinary carbon does little against chloramine, so the media has to be catalytic carbon, and lead needs its own stage. At 350 gallons a day a 100,000 gallon set lasts about 9 months.
Well with orange staining, 2 bathrooms, 3 people
- 2 bathrooms, 3 people, 1 inch main
- Private well
- Iron tested at 2 ppm, plus grit
9.4 GPM peak. A 3-stage 20 inch iron and manganese system behind a spin-down sediment screen.
Cartridge iron filters are rated for up to 3 ppm iron, so 2 ppm fits. Wells push sand that clogs a 5 micron cartridge, so a reusable 50 micron spin-down screen goes first. At 210 gallons a day the 100,000 gallon set reaches its 12 month limit before its gallon rating.
Frequently asked questions
What size whole house water filter do I need?
Size it by peak flow. With one 2.5 GPM shower per bathroom plus two faucets running, a 1 bathroom home peaks near 7 GPM, 2 bathrooms 9.4, 3 bathrooms 11.9 and 4 bathrooms 14.4. Up to about 10 GPM, 10 x 4.5 inch cartridges work; above it, use 20 x 4.5 inch cartridges or a tank system rated for the flow.
Should I get a 10 inch or 20 inch whole house filter?
A 20 x 4.5 inch cartridge holds about twice the media of a 10 inch one, so at the same flow it drops less pressure and lasts about twice as long. iSpring rates its 10 inch sediment and carbon set at 50,000 gallons and its 20 inch sets at 100,000. Pick 10 inch for 1 to 2 bathrooms and tight spaces, 20 inch for 3 or more bathrooms.
How often do you change a whole house water filter?
Divide the cartridge's rated gallons by what your household uses. At about 70 gallons per person per day, 4 people use 8,500 gallons a month: a 50,000 gallon set lasts about 6 months and a 100,000 gallon set about 12. Change sooner if pressure drops, and never go past the maker's month limit, even with gallons left.
Does a whole house carbon filter remove chloramine?
Standard carbon blocks remove chlorine well but chloramine slowly. For chloramine you need catalytic carbon (sometimes paired with KDF) and a system whose maker lists chloramine. Your utility's annual Consumer Confidence Report says which disinfectant it uses.
Do I need a 3/4 inch or 1 inch whole house filter?
Buy 1 inch ports when you can; most Big Blue systems use them and connect to a 3/4 inch main with reducing fittings. A 3/4 inch copper line carries about 12 GPM at the 8 ft/s velocity limit the Copper Development Association gives for cold water, and 1 inch about 20 GPM, so a 3 bathroom or larger home is better served by a 1 inch main and ports.
Will a whole house water filter lower my water pressure?
A little, more as cartridges load up. A system rated above your peak flow, with 1 inch ports and 20 inch cartridges for larger homes, keeps the drop small. A filter rated under your peak, or a clogged sediment cartridge, is when you notice it in the shower.
Does a whole house filter soften water?
No. Sediment and carbon filters do not remove calcium and magnesium. If you have hard water, add a softener after the filter so the carbon removes chlorine before it reaches the softener resin.
Can a whole house filter remove lead or PFAS?
Some can, with a dedicated stage: iSpring's lead filters are rated from 100 ppb down to 15 ppb, and its PFAS cartridges are SGS-tested to reduce up to 99%. These are maker claims tested by third-party labs, not NSF 53 or 58 certifications. For drinking water, a certified reverse osmosis system at the kitchen sink is the stronger second layer.
Marcus Reed
Founder and Editor, CrunchYourDollars
Marcus Reed builds the sizing tools on CrunchYourDollars. He is a software engineer with a long-running PC hardware and power supply habit, which is where the watts, watt-hours and surge math on this site comes from. Product specs are pulled from manufacturer data sheets, electricity rates from the U.S. Energy Information Administration, and water chemistry rules from the Water Quality Association. He is not a licensed electrician or plumber: the tools show the math and the matching models so you can make the call, and anything involving your electrical panel should be checked by a licensed pro.
More about CrunchYourDollars and how we researchGet notified when we add tools
An occasional email when a new sizing tool goes live or the product database is refreshed. No spam, unsubscribe anytime.