Open toilet tank against dark tile: a fill valve on the left, and a chain from the flush lever down to a red flapper beside a white overflow tube

Toilet flappers & running toilets

Which toilet flapper do I need?

9 sources checked

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Quick answer

Measure the round drain hole the flapper sits on. Fluidmaster says a hole of about 2½ inches takes a 2-inch flapper and about 3½ inches takes a 3-inch flapper. No ruler? Korky's rule of thumb: orange or baseball size is 2-inch, grapefruit or softball size is 3-inch. Then match the frame (all-rubber or solid plastic) and pick an adjustable flapper for a 1.28 or 1.6 gallon-per-flush toilet.

Where to buy: genuine parts from the maker. Pick the size you measured; the last two fit both sizes.

Fluidmaster 502 (2-inch) Fluidmaster 5403 (3-inch) Fluidmaster 523A (2- and 3-inch) Korky 3020 Fit-All (2- and 3-inch)

Our diagram, based on the measuring rules in Fluidmaster's and Korky's flapper-size guides. Sizes are approximate; when in doubt, take the old flapper to the store.

Three things decide the flapper

Fluidmaster sorts flappers by size, frame and type. Get the size right first; Korky calls it "the most important factor" for a universal replacement.

What to check	Options	How to tell
Size	2-inch or 3-inch	Drain hole about 2½ in or 3½ in (Fluidmaster). Old flapper about 3 in or 4 in across. Korky's Fit-All video uses 2¾ in as the cut-off. See 2-inch vs 3-inch.
Frame	Flexible (all-rubber) or solid (hard plastic frame)	Fluidmaster: all-rubber flappers stretch to fit odd or angled flush valves and valves without mounting posts. If you already have a plastic-framed flapper, a solid-frame one is a good replacement.
Type	Adjustable or non-adjustable	Fluidmaster: adjustable flappers are for 1.28 and 1.6 gallon-per-flush toilets (1994 on). Non-adjustable ones are for older 3.5 and 5+ gallon toilets and come only in 2-inch.

Toilet age is only a hint, and the makers disagree on the year: Fluidmaster says most toilets before 2005 take a 2-inch flapper, Korky says most made before 2000 do. The measurement decides.

Fluidmaster also says its 3-inch flappers come only with a solid frame, so in its range an all-rubber flapper is a 2-inch part.

Guides

Guide2-inch or 3-inch flapper?Measure the drain hole or the old flapper. Takes a minute.Read guide

Fix guideStill running after a new flapperFill valve, chain, leak test, valve seat or the wrong flapper.Read guide

Fix guideFlapper closes too fastSet the adjustable flapper, chain and water level for a full flush.Read guide

No flapper in the tank?

Some toilets use a tower or canister flush valve that lifts straight up instead of a hinged flapper. Korky says these take "a replacement seal designed for that specific model", so a universal flapper won't fit. Look for the toilet maker's name and model number (often printed inside the tank or under the lid) before you shop.

Didn't measure? Universal 2- and 3-inch flappers

Both big repair-part makers sell one flapper that converts between sizes: Fluidmaster's 523A Super Flapper, which Fluidmaster lists for 2-inch and 3-inch flush valves, and Korky's 3020 Fit-All, which "quickly converts from a large 3-inch to a standard 2-inch". Korky still says "it is always better to get the correct size", so measure when you can.

Why bother: the EPA's WaterSense program says most toilet leaks come from old or worn-out flappers, and that household leaks can waste 180 gallons a week. A flapper is a cheap part.

Before you start: shut off the supply valve behind the toilet and flush to empty the tank. Fluidmaster warns not to use in-tank drop-in cleaners containing bleach or chlorine because they damage tank parts and void its warranty.

How we work: every size, date and fit statement on these pages comes from the part maker's own guide, instructions or product page, or from the EPA. Each page lists its sources, and where the makers disagree we say so.

Questions people ask

Are all toilet flappers universal?

No. Fluidmaster says there are universal designs that replace most flappers, plus specialty flappers for specific flushing systems. Toilets with a tower or canister flush valve take a seal made for that model, not a flapper (Korky).

Are most toilet flappers 2-inch or 3-inch?

Fluidmaster says most toilets made before 2005 use a 2-inch flapper and most made after use a 3-inch one. Korky puts the change around 2000. Measure the drain hole to be sure: about 2½ in is 2-inch, about 3½ in is 3-inch.

Can one flapper fit both sizes?

Yes. Fluidmaster's 523A Super Flapper and Korky's 3020 Fit-All both convert between 2-inch and 3-inch. Korky still says it is better to buy the correct size when you can measure.

Sources

Fetched and checked 2026-10-21. Parts and instructions change; check the maker's instructions for your part before buying.