2-Inch vs 3-Inch Toilet Flapper: How to Tell

Buy links on this page go through our /go/ redirects to the manufacturer or retailer. We earn nothing from them today; that may change. Disclosure.

Quick answer

Shut off the water, flush, and measure across the round drain opening under the flapper. Fluidmaster says about 2½ inches means a 2-inch flapper and about 3½ inches means a 3-inch flapper. Or measure the old flapper itself: about 3 inches across is a 2-inch flapper, about 4 inches across is a 3-inch. The size names refer to the flush valve, not the rubber you're holding.

Where to buy: genuine parts from the maker, by the size you measured.

Fluidmaster 502 (2-inch) Fluidmaster 5403 (3-inch) Korky 3020 Fit-All (both sizes)

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.

Measure the drain hole

Turn off the supply valve behind the toilet and flush. Hold the handle down to drain as much water as you can.
Unhook the chain and pull the old flapper's ears off the pegs on the overflow tube.
Measure straight across the drain opening at the bottom of the tank.
About 2½ in: buy a 2-inch flapper. About 3½ in: buy a 3-inch flapper (Fluidmaster's figures).

Korky's install video for its Fit-All kit uses a single cut-off: an opening smaller than 2¾ inches is a standard 2-inch, larger than 2¾ inches is a large 3-inch. That fits with Fluidmaster's numbers, since 2¾ sits between 2½ and 3½.

Or measure the old flapper

Fluidmaster calls this "the simplest way": measure the width of the flapper from end to end. 3 inches across: buy a 2-inch flapper (like Fluidmaster's 502). 4 inches across: buy a 3-inch flapper (like its 5403). That's why people buy the wrong one: a "2-inch" flapper is wider than 2 inches.

No ruler? The ball test

Korky's quick reference: if the opening (or the old flapper) is about the size of an orange or a baseball, you need a standard 2-inch flapper. If it's more like a grapefruit or a softball, you need a large 3-inch one. Taking the old flapper to the store works too.

Sources disagree on toilet age

Sources disagree

Fluidmaster says "the majority of toilets predating 2005 will be a 2-inch flapper" and most made after 2005 are 3-inch. Korky says most toilets made before 2000 need a 2-inch, and that 3-inch flappers "have become popular since the year 2000". Use age only as a hint; the measurement decides.

Match the frame too

Size isn't the only fit issue. Fluidmaster makes two frame styles. All-rubber (flexible) flappers stretch to fit odd-sized or angled flush valves and valves without mounting posts. Solid-frame flappers have a hard plastic frame that centers the seal, but "does not work with all flush valve drains". If your old one had a plastic frame, a solid-frame replacement is a good bet. Fluidmaster's 3-inch flappers come only in solid frame.

In the store without a measurement

Korky says "it is always better to get the correct size", but if you didn't measure, its 3020 Fit-All converts between 3-inch and 2-inch. Fluidmaster's 523A Super Flapper does the same. Both makers make universal flappers, but Fluidmaster notes that some flush systems need specialty flappers, and tower or canister flush valves take a model-specific seal instead (see which toilet flapper do I need).

New flapper on and the toilet still runs? See toilet still running after a new flapper. Flush too weak? See flapper closes too fast.

Sources

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