What Size of Toilet Flapper Do You Need? The Guide

How Do I Know the Size of my Toilet Flapper?

Toilet flappers do last for a long time but after years of continued usage they tend to warp/bend resulting in a running toilet. To replace your toilet flapper, you must first know its size so that you can replace it with an exact one.

Unlike in the 1900s when toilet flappers were all universal, today they are not. Toilet flappers vary in size between 2 and 4 inches, have different designs and are also made from different materials.

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To determine what size of toilet flapper you need, turn off water to the toilet, flush it and remove the old toilet flapper. Measure the diameter of the flush valve opening at the bottom of the tank. It will be 2 inches in old toilet models but newer models will have a 3 or 4-inch flush valve.

If you get a 2-inch reading, you will need to order a 2-inch toilet flapper and the same also applies if you a get a 3 or 4-inch reading.

Korky and Fluidmaster manufacture standard/universal toilet flappers that are as good as those made by the original toilet manufacturers. As long as you know the size of the toilet flapper you need, the toilet flappers can be installed in any toilet.

Since a toilet flapper sits on top of the flush valve opening, I find that measuring the size of the flush valve opening is the best and easiest way to determine what size of toilet flapper you need.

Although you can still measure the toilet flapper itself, it is usually conical-shaped which makes measuring it a bit difficult. The flush valve opening is flat and all you need to do is just place a measuring tape on top of it and read the measurement.

If you don’t have a measuring tape or don’t feel like measuring the toilet flapper yourself, there is a simple trick you can use to know if you have a 2-inch or a 3-inch toilet flapper.

Do you have a 2 or 3-inch Toilet Flapper?

To know if you have a 2 or 3-inch toilet flapper, compare the size of the flush valve opening to that of a baseball and softball. If it is the size of a baseball or orange fruit, you need a 2-inch toilet flapper while if it is the size of a softball or grapefruit you need a 3-inch toilet flapper.

Another easy way to know what size of toilet flapper you need is to remove your old one and take it with you to the nearest home improvement store. Home improvement specialists will not even need to measure but will give you an exact replacement.

Your toilet’s water consumption can also help you determine what size of toilet flapper you need. Toilets with a consumption of 1.28 gallons per flush will have a 3-inch flush valve. 1.6 GPF toilets may have a 2 or 3-inch toilet flapper but 3.5 GPF will definitely have a 2-inch toilet flapper.

If your toilet was manufactured before 2005 you may have a 2-inch toilet flapper. For toilets manufactured after 2005 (introduction of WaterSense toilets) you most likely have a 3-inch flush valve.

The reason toilets with bigger flush valves (and hence bigger toilet flappers were introduced is to allow a large amount of water to flow from the tank to the bowl within a very short period of time.

The sudden dumping of more water into the bowl creates an even stronger siphon and hence powerful flushing toilets. This allows the manufacturing of strong flushing toilets that uses less water at the same time.

Most modern toilets have a 3-inch flush valve while some like the American Standard Champion 4 have an even larger flush valve of 4 inches. A more experienced person can tell the size of a toilet flapper by just looking at it.

How to Measure the Size of Toilet Flapper

In order to know what size of toilet flapper you need, you will first need to remove it from the tank and measure it, or measure the flush valve opening.

These are the steps to follow:

1. Turn off Water to the Toilet

You can’t remove a toilet flapper without first turning off water to the toilet. Water will continuously run from the tank to the bowl via the flush valve.

You will see an oval-shaped knob on the wall behind the toilet. That is the toilet shut off valve. Turn it all the way clockwise. Push/pull shut off valves will need you to pull the knob outwards to turn off the water supply.

Flush the toilet and hold the flushing handle down to remove as much water as possible from the tank.

2. Remove the Toilet Flapper

  • Lift off the toilet tank lid and place it away in a safe place where it cannot fall of and break.
  • Disconnect the flapper lift chain from the flushing handle arm. Once disconnected just drop the lift chain inside the tank
  • The toilet flapper has 2 ears connected to 2 pegs on the flush valve. Unhook the flapper ears from the pegs and lift it off.
  • Place it on a bench.

As I had mentioned, there are 2 methods to measure the size of a toilet flapper. You can either measure the flapper itself of the flush valve opening. I will show you how to do both.

3. Measure the Flush Valve Opening Size

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  • Use a measuring tape or a small rule to measure the inside diameter of the flush valve opening.
  • If you get a reading of between 1.8 and 2.3 inches then you have a 2-inch flush valve. Proceed to buy a 2-inch toilet flapper as well.
  • A reading of plus or minus 3 inches indicates you have a 3-inch flush valve and therefore need a 3-inch toilet flapper.
  • A flush valve wider than 3 inches is a sign that you need a 4-inch toilet flapper.

4. Measure the Toilet Flapper

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Measuring the size of a toilet flapper is a bit tricky so you need to be very careful otherwise you will end up buying the wrong size of toilet flapper.

You can either measure the length of the cone, or the entire width of the flapper from end to end. I find measuring the size of the flapper from end to end to be more precise and easy

If you decide to measure the width of the cone only then the reading is straight forward. Buy a 2-inch flapper if you get 2-inch reading or a 3-inch flapper if you get 3 inches in reading.

If you decide to measure the width of the flapper from end to end, buy a 2-inch toilet flapper if you get 3 inches in reading and a 3-inch toilet flapper if you get 4 inches in reading.

After buying the new flapper, installing it is easy. Just place it over the flush valve opening and hook up the ears to the pegs then connect the lift chain to the flush handle arm.

It is important to get a good slack on the lift chain. If it is too tight, it may unseat the flapper off the flush valve resulting in leaks, while if it is too slack it will not lift the flapper completely during flushing and hence a weak flushing toilet.

Ideally, the lift chain should have a 1/2-inch slack.

The above guide refers to single flush toilets which use a toilet flapper. Dual flush toilets use a flush valve seal which I discuss in more detail in this post.

If you have a modern Kohler toilet, you could be having what is called a canister flush valve which also uses a flush valve seal. Read more about it in this post.

As I had mentioned earlier, there are a lot of things to consider when choosing a toilet flapper. For more information on the same watch this helpful video on You Tube by Tim.