A toilet flapper is the rubber seal at the bottom of your tank that lets water flow into the bowl

The flapper sits inside your toilet tank and lifts when you press the handle, allowing water to rush down into the bowl. When it wears out — usually after three to five years — water leaks slowly into the bowl even when nobody has flushed. You'll notice the toilet running on its own, or the water level dropping in the tank between flushes.

Replacing it is a straightforward job that takes about 15 minutes and costs between $5 and $15 for the part. You need only a flathead screwdriver and the new flapper, which you can find at any hardware store or online. The flapper comes in a few standard sizes, so you'll need to know which one fits your tank — we'll cover that below.

Key Takeaways

  • Turn off the water supply at the valve behind the toilet before you start, then flush to empty the tank.
  • The flapper is held in place by two small hooks on a rod that runs across the tank — you lift it straight up and off.
  • Flappers come in different sizes; bring the old one to the store or measure the opening at the bottom of the tank to get the right fit.
  • The new flapper slides onto the rod the same way the old one came off, and the chain reconnects to the flush lever arm.

Turn off the water and empty the tank

Look behind the toilet at floor level. You'll see a small valve with a handle — turn it clockwise until it stops. This shuts off the water supply to the tank. Then press the handle to flush; the tank will empty and stay empty because the water is now off.

If the valve is stuck or leaking, you can still do this job — just work quickly and have towels ready. If you can't turn the valve at all, you may need to call a plumber to replace it first, because a stuck valve often means it's failing.

Remove the old flapper

Look inside the empty tank. At the bottom center, you'll see a rubber or plastic disc — that's the flapper. A rod runs horizontally across the tank, and the flapper is held on by two small hooks, one on each side of the rod.

Lift the flapper straight up. It will slide off the rod easily. You may also see a chain attached to the flapper; unhook it from the small arm connected to the flush handle. Set the old flapper aside — you'll use it to find the right size replacement.

Get the right size flapper

Flappers come in two main sizes: 2-inch and 3-inch, measured across the rubber disc. Take the old flapper to a hardware store, or measure the opening at the bottom of your tank where the flapper sits. Most older toilets use 2-inch flappers; most newer ones use 3-inch.

If you're buying online or can't get to a store, you can also look up your toilet's model number (usually stamped on the back of the tank) and search for the flapper that way. Universal flappers that fit both sizes also exist, though they're less common and sometimes less reliable.

Install the new flapper

Slide the new flapper onto the rod, positioning it the same way the old one sat — centered at the bottom of the tank with the hooks on either side of the rod. It should sit flat and not tilt or catch on anything.

Reattach the chain to the small arm connected to the flush handle. The chain should have a tiny bit of slack — about a quarter-inch — so the flapper can seal completely when it closes. If the chain is too tight, the flapper won't seal and water will leak. If it's too loose, the flapper won't lift all the way and the flush will be weak.

Turn the water back on and test

Turn the valve behind the toilet counterclockwise to turn the water back on. The tank will refill. Once it's full, press the handle and watch the flapper lift and fall. The water should rush into the bowl, then stop completely when the tank empties and the flapper closes.

Listen for running water after the tank refills. If you hear a faint hiss or trickle, the flapper may not be seating properly — check that the chain isn't too tight and that the flapper is centered on the opening. If it still leaks after you've adjusted it, the flapper may be the wrong size or the tank opening may be damaged, and you'll need a different part or a plumber's help.

Frequently Asked Questions

How do I know if my flapper is actually broken?

The most common sign is a toilet that runs on its own or hisses quietly after you flush. You can also watch the water level in the tank — if it drops slowly even though nobody flushed, the flapper is leaking. Lift the tank lid and look at the flapper; if it's cracked, warped, or has mineral buildup that won't wipe off, it needs replacing.

Can I use a universal flapper instead of measuring?

Universal flappers work in many toilets, but they're less reliable than the correct size for your tank. If you go this route, test it carefully after installation. If the flush is weak or water leaks, switch to the proper size flapper for your toilet model.

What if the chain keeps coming loose from the flapper?

The connection point on the flapper may be worn or cracked. If tightening or repositioning the chain doesn't hold, the flapper itself is damaged and needs replacement. This is common in older flappers and is a sign the whole flapper assembly should come out.

Do I need to replace the whole flush valve if the flapper doesn't work?

Not usually. The flush valve is the large assembly at the bottom of the tank; the flapper is just the seal on top of it. Replace the flapper first. If water still leaks after a new flapper is installed correctly, then the valve itself may be damaged and need professional replacement.