What Size Drain Pipe For Shower?

Updating the shower in your bathroom is an exciting project with many options for a visually appealing and luxurious place to wash away the stress of the day. 

However, the unseen parts, in particular the drain and plumbing, are very important to install correctly to avoid complications such as flooding.

The minimum pipe size for a shower drain is 2 inches (5.08 cm), to allow water to drain quickly and properly. Shower and tub combinations can have a 1 ½ -inch (3.81 cm) drain connection. However, it is recommended to attach a 2-inch drain pipe to these as well, if possible.

This article will tell you about the factors for the installation of drain pipes, drain assemblies, and FAQs related to shower drains. Read on.

Standard Drain Pipe Size For Shower

The Uniform Plumbing Code is an excellent resource for ensuring your shower drain pipe size is up to code, safety, and environmental standards. You will see that a 2-inch drain pipe is standard for a shower. 

Why Use A 2-inch Drain Pipe

Shower stalls cannot handle flooding like bathtubs due to the low lip or edge around the unit. Angles, pressure, and open lines (no clogs) of piping systems affect flow and drainage, but in general, a larger pipe will drain faster than a smaller one. 

For example, a 2-inch PVC drain pipe can handle 55 gallons per minute, whereas a 1.5-inch PVC drain pipe can only handle 35 gallons per minute. 

A shower head generally allows a maximum of 2.5-gallons of water flow per minute of use. To avoid a quick flood or pooling, the drainage system must pull this water out quickly and effectively.

Even if you do not have 2-inch connections within your current plumbing, you can still use a 2-inch drain pipe. You just need to make sure you have plumbing parts to connect all of the pieces seamlessly and avoid leaks. 

If you decide to use a drain pipe smaller than two inches, then you run the risk of flooding the shower pan while you are showering.

Factors For Installing Shower Drain Pipes

When installing a drain pipe for the shower, several factors will affect how you go about this task. 

Consider the following:

  • Drain: The sizing of your shower base’s drain connection point generally is 2-inches. However, it could be different in customizable situations.
  • Tub to Stall: If you are converting from a shower and bathtub combination to a shower stall only, the pipe connections may be different. Shower and tub combinations use 1.5-inch drain pipes. 
    • If you have access to the interior plumbing you may wish to replace this pipe with a 2-inch. 
  • Older Pipes: Older homes may have smaller or different pipes and connection materials. You may need to replace or fit pipes mismatched together with connecting joints or reducers.
  • Manufacturer Design: A brand new shower pan may also have manufacturer’s recommendations about what will work best with a prefabricated shower pan. Most are fitted for a 2-inch connection.
  • Access: If there is no access panel or basement access to the bathroom’s plumbing, you may need to cut into the drywall or ceiling. You may need professional support to take on this part of the task if you are without access below or nearby to the pipes.
  • Fit: Once you have all of your parts, check that they all fit together with the piping and drain assembly in your work area before you permanently affix them together. 

Drain Assembly

There are three types of drain assemblies: compression, solvent-weld, and tiled. These assemblies work with the drain pipe to carry water out. 

The drain cover has holes to keep large items from falling into the drain and causing a clog, yet allows for water to flow through quickly to the drainage system.

The standard shower drain cover size has an outer diameter of about 4 ¼-inches (11.4 cm) and an inner diameter of 3-inch to 3 ½-inch (7.6 – 8.9 cm) in size.

If you are replacing the drain pipe, much like a sink, you should also remove the old drain, and install a new one. It is likely the old connections are welded into place, and it is easier to replace them with all new connections. 

If you decide to cut pipes off, you will end up with shorter pieces that you need to accommodate to make sure it functions and connects properly. 

It is important to note that if you are installing a new shower floor, the floor slopes towards the drain to encourage the wastewater to flow out. 

Types of Drain Assemblies

Compression Drain Assembly

This style is used for easier installation in areas where you do not have access to a crawl space or basement location underneath the drain. These drains are attached to the shower drain pipe with nuts and washers and a rubber compression gasket. 

Generally, these are made of PVC, but can also be ABS or brass materials. In turn, these drains can connect with shower bases that are steel, fiberglass, or acrylic.

Solvent-Weld Drain Assembly

A shower drain that is welded, or glued with solvent to a drain pipe, is best only when you have access to a crawlspace or basement piping area. 

These drain assemblies may be made of ABS or PVC plastic and can work with shower bases made of steel, acrylic, and fiberglass. If possible, match the drain assembly material with the same material of the 2-inch drain pipe. 

Fitting together an assembly with a pipe using solvent adhesion can be challenging if the measurements are inaccurate. Test-fit the pieces before gluing them together. It will be very difficult to take them apart for readjustment once welded.

The assembly will have a straining cover, parts to screw together to fit into the openings, and a smooth socket to glue to the drain pipe. There will also be washers to tighten parts into place as well. 

Tile Drain Assembly

If you have a tiled shower floor, the drain assembly consists of several pieces that are put in along with the tile installation. If you need to install a new drain assembly after a shower pan is in place, you will need to remove tile as well, making this a bigger project. 

There is a waterproof liner in between two bolted flanges to protect the mortar. The strainer assembly sits at the top of the drain system. 

Generally, if a professional is installing the tile shower floor, this type of drain assembly is done for you. You can still request a 2-inch drainage pipe to be part of this system.

Connecting Pipes

When pipes are designed to seamlessly fit and connect, the process is relatively simple. Plumbers tape, joint compound, and connecting pieces such as elbows, P-traps, and coupling are part of the system.

When pipes are of different sizes, adapters, called reducer bushings can be used. Again, you will need a waterproof compound to seal any joints and keep water from leaking.

You should measure the diameter of the piping that is already in place, the diameter of the drain assembly, and the length of pipe needed to make sure you are getting everything you need at the hardware store. 

If the current piping that leads to the main line has any corrosion or defects, consider if it needs to be replaced. Ask a store representative to help you out and ensure you have all of the pieces you need. You may need a PEX or PVC cutter or hacksaw for cutting pipes.

Referencing a shower drain pipe diagram is going to be helpful if you are doing this installation yourself. It would be beneficial to test the system as you connect. 

Pour some water into the piping before you attach the drain assembly to make sure there are no leaks. Then, when the drain assembly is in place, run the shower to make sure water is not pooling.


Can you use 1 ½ pipe for shower drain? 

You can use a 1 ½ pipe (3.81 cm) for a shower drain. However, you run the risk of flooding or pooling water. Additionally, you may not meet the plumbing code for your area.

Can I use a 2-inch drain pipe for my shower and tub unit?

This type of unit typically has a 1.5-inch (3.81 cm) drain pipe. 

You can install a 2-inch (5.08 cm) drain pipe for your shower and tub unit. It will drain water faster when showering, keeping water from pooling at your feet.

Are shower drain covers the same?

Shower drain covers are not the same. They can vary in size and have different amounts of drain holes. The standard size is 2-inches (5.08cm), but some options are 3-inches (7.62 cm) or larger.

Choose the size that correlates with your shower floor and plumbing connections. If you choose one with more holes, it will drain faster. 

Can a shower drain be covered?

A shower drain can be covered with a hair trap to keep lint and hair out of the plumbing.

The trap will need to be cleaned and cleared from debris, hair, and soap scum to work efficiently. A dirty trap will allow water to pool at your feet.

Can a toilet and shower share the same drain pipe?

A toilet and shower are permitted to share a drain pipe in the United States. However, they cannot share a waste trap arm in order to keep the shower sanitary.

Key Takeaways

A 2-inch (5.8 cm) drain pipe is the minimum size drain pipe to effectively drain wastewater away. When installing drain pipe, ensure that all connections are tight and waterproof, regardless of the connecting parts’ sizes. 

Contact a plumbing professional for any questions or support.

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