How to Identify Your Toilet Brand and Model [2026]

May 30, 2026 9 min read

A leaking flapper costs $4 to fix and a fill valve costs $10, but only if you buy the right one. Buy the wrong size flapper or a generic fill valve that doesn’t seat in your tank’s flush-valve opening and you’ve added a return trip to the hardware store, a second weekend, and zero progress. Knowing how to identify your toilet brand and model before you start the repair is the single highest-leverage step in any toilet fix.

The good news: most toilets stamp the model number somewhere you can read it in 30 seconds with a flashlight. The catch is that no manufacturer agrees on where to put it, so you have to know all five of the common locations. This article walks through them in order from “easiest” to “you may need to call customer service,” with brand-specific cues for the five most common residential toilet brands – Kohler, TOTO, American Standard, Gerber, and Mansfield.

Method 1: Inside the Tank, Back Wall Near the Waterline

This is the most common location and the place to start. Take the tank lid off (lift straight up, set it gently on a towel – porcelain chips easily). Shine a flashlight at an angle across the back wall of the tank, just above and below the waterline.

What you’re looking for: a stamped, molded, or ink-printed model number. American Standard tank numbers are four digits and sit on the back wall near the water-level mark, either stamped into the china or printed as a barcode label. Kohler tank numbers are molded into the china or stamped in blue or black ink, and a K prefix may or may not appear in front of the base number. Gerber tank model numbers sit on the back wall near the waterline alongside a cast date and a barcode/serial label Gerber calls the “D and S Code.”

For TOTO, look at both the back wall AND the right-hand wall opposite the trip lever – TOTO model marks are stamped or engraved into the china in both locations depending on the model. TOTO model numbers commonly combine letters and a three-digit number like CST854, ST743E, or MS974CEFG.

trip lever replacement part shown for inline reference

If mineral deposits or water staining make the stamp hard to read, wipe the back wall with a cloth before getting close with the flashlight. Kohler explicitly notes that dirt remaining in the depressions can actually make an impressed number MORE visible, so don’t scrub the area completely clean before reading it.

Method 2: Underside of the Tank Lid

Flip the tank lid over (carefully – this is the most expensive part on the toilet to replace). Look at the underside.

Tank lids often carry a separate part number from the tank itself. For Kohler, the underside of the lid has a part number specific to the lid, not the toilet – useful for ordering a replacement lid, but not enough to identify the toilet’s internal repair parts. For Mansfield, the tank model number can appear under the lid, on the back wall of the tank, OR on the bottom of the tank itself. For older or obscure toilets, the lid underside is sometimes the only legible marking left.

Photograph anything you find before putting the lid back. A plumber or customer-service rep can often work backwards from a lid part number plus photos of the internal flush valve to identify the original toilet.

Method 3: Under the Bowl Rim or Between Seat Bolts

The bowl has its own identification, and bowl numbers are easy to confuse with tank numbers. For a two-piece toilet, the tank and bowl can come from different model lines if a previous owner replaced one half – so knowing both numbers matters when ordering parts that span the tank-to-bowl interface (gaskets, tank bolts, certain flush valves).

Kohler two-piece bowl numbers are molded into the underside of the bowl flange. Gerber bowl numbers sit under the rim of the bowl – use a smartphone camera or small mirror to read it while installed. Many modern toilets also stamp the manufacturer name in small print on the bowl between the two seat bolts (lift the seat to expose this area).

Ignore the brand name printed on the toilet seat itself. The seat is frequently replaced with an aftermarket part and may not match the toilet’s manufacturer at all. Mistaking the seat brand for the toilet brand is one of the most common identification errors.

Method 4: Brand-Specific Cues

When the tank or bowl stamp is faded, missing, or covered by a tank liner (Kohler’s “Insuliner” model in particular), brand-specific visual cues can narrow the search.

Kohler: four- or five-digit tank numbers, optional K prefix, blue or black ink stamps, canister-style flush valves on some models, generation suffixes like AA, AB, or BA after the color code. Kohler offers a beta photo-upload tool called Kohler Scout that can match a full-toilet photo to a model.

American Standard: four-digit tank marks. Numbers beginning with 2 indicate a one-piece toilet; numbers beginning with 4 indicate a two-piece tank. The string XXX in parts diagrams is a placeholder for the color/trim suffix – a suffix often matters when ordering visible china or trim.

TOTO: look for letters plus a three-digit number. ST = tank, CT = bowl, CST = gravity-toilet pair, MS = toilet sold with seat included. Suffix letters: E = E-Max/Eco 1.28 gpf (different flush valve), G = Sanagloss/CeFiONtect glaze, R = right-hand lever, M = Dual-Max dual flush. Color codes start with # – #01 is Cotton White, #11 is Colonial White.

Gerber: tank numbers in 28-xxx format, bowl numbers in 21-xxx format. Line names like Aqua Saver, Maxwell, Viper, and Avalanche group different tank/bowl pairs – shape comparison can help when the stamp is partial.

Mansfield: typically three-digit model numbers, many starting with 1 for two-piece or 7 for one-piece; newer models are four digits starting with 3. Mansfield often notes water consumption (gpf) inside the tank.

Pressure-assist toilets: Flushmate and Sloan systems are visually distinct – the tank contains a sealed black vessel instead of open water. The Flushmate series number is on a blue sticker at the top of the pressure tank, separate from the porcelain toilet’s model number. Pressure-assist tanks need their own number AND the porcelain toilet number to order parts correctly.

Method 5: Manufacturer Photo Tools and Customer Care

When stamps are unreadable or the toilet is older than 15 years, the manufacturer is your last identification step before guessing.

Kohler’s Find a Service Part page supports a three-step flow: identify the product, view the parts diagram, select the genuine part. Kohler Scout (beta) accepts a photo upload and attempts to identify the model. Mansfield’s parts sellers explicitly ask for tank/parts photos when the number can’t be found.

American Standard’s support is FAQ-based – their model-number help points you back to the four-digit tank number on the back wall. TOTO USA has product FAQs plus PDF parts manuals you can search by model string. Gerber’s model-number help page walks through tank, bowl, cast date, barcode, and serial locations specifically.

A short ID phone call to manufacturer customer service can be free, but if it ends with “we need a plumber to look at it in person,” budget $75-$150 for a plumber diagnostic/service-call visit (Modernize’s 2026 plumbing cost guide).

How to Identify Your Toilet: The Quick Decision Tree

If you’ve worked through the methods above and want to know what to do with what you found:

Tank model number is legible: that’s the most useful number. Most repair parts are determined by the tank number marked inside the tank.
Only the bowl number is legible: good for bowl-specific parts (rim gaskets, bowl-to-floor seals); contact the manufacturer with the bowl number to back into the tank model.
Only the lid number is legible: good for lid replacement; not enough for internal parts. Treat the lid number plus full-toilet photos as a customer-service ticket.
Nothing is legible but the manufacturer logo is visible: use brand-specific visual cues above to narrow the line, then try the manufacturer’s photo tool (Kohler Scout, manufacturer parts FAQ).
No legible markings AND no logo: the toilet is either very old or generic. Move to universal “will fit” parts (Method 6 of this guide is implicit – universal flapper kits work on ~99% of toilets per Korky’s specification) OR replace the whole fixture if it’s an old high-gpf model anyway.

flapper replacement part shown for inline reference

What to Do If You Still Can’t Find the Brand

Three fallback paths, in order of preference:

A disciplined photo set. Photograph the whole toilet from front, side, and above. Photograph the tank with lid on and off, the underside of the lid, the inside back wall, side walls, bottom of tank, flush valve, fill valve, trip lever, bowl rim, and every number, barcode, label, or date mark. Send the set to manufacturer customer service or upload to Kohler Scout if you suspect Kohler.

fill valve replacement part shown for inline reference

Universal “will fit” parts. Fluidmaster’s 400H Performax fill valve has universal compatibility with most 2-inch and 3-inch toilets and adjusts from 9 to 14 inches in height. Korky’s universal fill-valve and 2-inch flapper kit advertises a fit on 99% of toilets. Danco and BrassCraft sell similar universal toilet repair kits. Universal parts work for the high-frequency causes (worn flapper, failing fill valve) but NOT for proprietary canister/tower flush valves, pressure-assist systems, or toilets with non-standard mounting hardware.

Replace the whole toilet. Reasonable when the porcelain is cracked, the tank or lid is unavailable, the pressure vessel is obsolete, the fixture is an old high-gpf model with repeated part failures, or the repair would require discontinued parts at premium prices. Rebuilding a toilet runs $250-$600 (Fixr); a new water-efficient toilet starts around $150 and goes up.

What to Do Next

Once you have the model number, the per-issue repair articles tell you what to actually buy. The Pillar 2 cluster – including Why Is My Toilet Running? 6 Common Causes and the per-issue toilet repair articles publishing on a rolling cadence – all start with “what’s your model” before they recommend parts. Bookmark the Toilet Repair Guide (Pillar 2 hub) as the index, or subscribe at the bottom of any guide page for one notification per new article.

For the faucet equivalent – “How to Identify Faucet Brand and Model” – the same identification logic applies. See How to Identify Your Faucet Brand and Model for cross-fixture identification patterns that work for faucets, valves, and supply fittings.

Sources

Educational content only. Not a substitute for licensed professional advice. Local plumbing codes vary by jurisdiction. Use of any guidance from this guide is at your own risk.

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