Guide to Toilet Flange Dimensions (with Drawings)

A toilet flange is a plumbing fitting that connects the toilet to the floor and connects the pipe to the drainage system. These functions are vital in the correct running of a toilet, so it’s important that you use the right type of flange for your toilet and pipework. Here we look at the different types of toilet flanges and toilet flange dimensions.

How Does a Toilet Flange Work?

A toilet flange is placed just under the floor level in the bathroom and connects to the pipe, which carries water away to the property’s drainage system.

The flange is screwed in place, and then the toilet itself can then be screwed onto the flange. This provides a secure fit that will prevent the toilet from shifting out of place, and it also means the toilet won’t have to be screwed directly to the flooring, which can damage tiles.

The flange includes a wax ring that helps to seal the gap between the base of the toilet and the closet bend, which is necessary to prevent leakages. The toilet flange will need to be the right size to fit with the existing pipework in your home, therefore ensuring water cannot seep out from any poorly fitting parts.

Types of Toilet Flange


Plastic flanges are a popular choice because they are inexpensive, lightweight, strong, and won’t rust or corrode. They are the most popular choice of material for toilet flanges and are suitable for both residential and commercial use. The one drawback of plastic flanges is that they can collapse under extreme pressure from bulky waste or high water levels.


Copper is a good choice for plumbing parts because it is antifungal and antibacterial. It is resistant to corrosion and is strong and sturdy, though it can be expensive and difficult to install.


Brass flanges are heat resistant, strong, and durable but are prone to rust. They come in a wide range of sizes and types, including deep seal and offset shapes.


Aluminum flanges are lightweight and durable, as well as resistant to corrosion. However, they are not as strong as other types of metal toilet flange.

Cast Iron

Cast iron toilet flanges are designed to be used with cast iron pipes. They have a longer shape which allows them to fit deeper into the drain, making them useful for drain pipes that are located beneath the subfloor. This is a very strong type of toilet flange which comes in various sizes, but it is quicker to rust than any other type.

Stainless Steel

This type of toilet flange is resistant to rust and corrosion and is more lightweight than most other metal flanges.

Toilet Flange Diameter Sizes

Toilet Flange Diameter Sizes


The most common size of toilet flange you will find is the 4×3. This is the type you are most likely to encounter in a hardware store, as they tend to dominate the market in toilet flanges. The ‘4×3’ name is a reference to the diameter measurements of the upper and lower parts of the flange.

The top section of the flange which connects to the toilet has a measurement of 4 inches across, while the bottom part which connects to the drain will measure 3 inches across. The lower section of the flange measures 3 inches because this is the size of the standard 40 pipe used for plumbing toilets in most homes, therefore providing an easy and secure connection.

The advantage of having 4 inches of diameter on a toilet flange is that it allows for a little extra clearance space when the water leaves the toilet and a minimized risk of water being able to seep back through the wax ring in the future.

3 inch

This type of flange has a diameter of 3 inches on both the upper and lower parts. Like the 4×3 flange, it will work with a 40 pipe which is also 3 inches in diameter. If your pipework is not assembled with standard 40-size pipes, you will need a different-sized flange.

Although 3-inch toilet flanges are less widely available compared to 4×3 flanges, they are a perfectly suitable choice for installing in bathrooms providing they fit the pipes. The only minor disadvantage of this size of toilet flange is that a little more pressure is put on the wax ring when water passes through the slightly smaller pipe; however, these are designed to cope with pressure, and so this very rarely causes an issue.


There are some instances where you may need a non-standard-sized toilet flange, for example, if your pipes are a non-standard measurement. This can happen in older homes or if pipes made from different materials have been used. In some instances, you can use a regular-sized toilet flange with an extension kit, or you may need a toilet flange that has a larger or smaller diameter opening than usual.

Toilet Flange Shapes and Sizes

Toilet Flange Shapes and Sizes


Regular toilet flanges are typically around 5 inches in length. They are designed to fit inside and around the opening of the pipe, which is situated under the floor. This is the type of toilet flange most homeowners will need for their toilet.

Deep Seal

This type of toilet flange will have a length of around 12 inches. This added length compared to a regular toilet flange means that it will reach much deeper into the pipe.

The benefit of this is that the toilet has increased protection against leakages; however, for most residential use, this is an unnecessary addition. It is more likely to be used in public toilets, which experience higher levels of traffic. It can also be more complex to install.


This is a type of toilet flange that can make installation much easier if the toilet is positioned in an awkward place, for example, if the pipe opening is very close to a wall. An offset toilet flange will have an elbow bend which provides a solution to these kinds of issues, allowing adjustments to be made.