Plumbing Dimensions for the Bathroom

If you’re having some major plumbing work done in your home, or are doing it yourself, the toughest part of the job may be what’s called the “rough-in.” This is the part of the job where the sink, tub, or faucet get connected. If the rough-in is correct, the job will be about 90 percent done. This doesn’t have to be an intimidating task, however. There are a set of accepted rough-in measurements for sinks, toilets, and tubs/showers. Additionally, manufacturers of these fixtures often provide specifications in their guides. It’s important to check the standard dimensions against the manufacturer’s specifications to make sure they line up for your installation.

Plumbing Dimensions for the Bathroom


Centerline: This term is used frequently in plumbing. Essentially, it’s an imaginary vertical line put through a key point, usually the drain pipe. For instance, if two pipes are instructed to be 10 inches apart, you measure 10 inches between the centers of the pipes, not 10 inches between the edges of the pipes.

Base Floor Height: This refers to the subfloor if it’s new construction, or the finished flooring, if it’s a remodel.

Dimensions should be considered guidelines, as they can change. The instruction manuals that come with whatever you’re installing will have more precise dimensions.

Toilet Sink Shower/Tub
Supply Line (Vertical) 8 1/4″ 2″ to 3″ higher than drain pipe 80″ shower; 20 to 22″ tub; spout 4″ above tub rim
Supply Line (Horizontal) 6″ max from center 4″ to left and right of center 8″ apart
Discharge/Drain Hole from Back Wall 12 1/2″ N/A 14″
Discharge/Drain Hole (Vertical) 0″ 16″ to 20″ 0″
Fixture (Side to Side Buffer) 15″ to 18″ min 15″ to 20″ min 18″ min
Fixture (Front Buffer) 21″ min 21″ min 18″ min


Supply Line: In Terms of height, eight and a 1/4 inches above the floor; cold-water-only pipe creates one hole between five and 10 inches above the floor. For the horizontal supply line, it should be measured from the centerline running vertically through the center of the toilet; the supply line hole should be six inches to the side of the centerline; check the toilet to confirm location water supply connection.

Discharge Hole (back wall): Offset hole from the back wall by 12 and a 1/2 inches

Discharge hole (vertical): Drain located at floor height; distance is zero

Fixture (side-to-side buffer): This should be measured from the center of the toilet to either side, minimum clearance is 15 inches to any wall or other fixture; 18 inches recommended if the layout of the bathroom permits

Fixture (front buffer): Measured from the front rim of toilet forward, minimum clearance is 21 inches to the nearest obstruction; 30 inches recommended


Supply line (height): Two holes; vertically, both are about two-to-three inches above the drain pipe

Supply lines (horizontal): Two holes; one hole is four inches to the right of centerline; other is four inches to left of centerline

Discharge hole (vertical): About 16-to-20 inches above the floor; drain pipe to be the vertical centerline

Fixture (side-to-side buffer): From centerline, 15 inches minimum, 20 inches recommended

Fixture (front buffer): Minimum distance to nearest obstruction is 21 inches; 30 inches recommended

Placement of sink: Vertically, the sink should be about 31 inches above the floor, measured to the rim of the sink

Shower and Bathtub

Shower supply (vertical): 80 inches from the floor; where shower arm will go; showerhead will be about 65 to 78 inches above the floor

Tub supply (vertical): Faucet valves should be 20-to-22 inches above the floor; horizontally, each faucet goes four inches to the right/left of centerline; tub spout four inches above the rim

Discharge hole from back wall: Place drain on centerline; opening for drain access can be between 10 and 14 inches offset from framing, and 6 to 8 inches wide

Discharge hole (vertical): Drain located at floor height; distance is zero

Fixture (side to side buffer): 18 inches minimum required buffer

Fixture (front buffer): 18 inches minimum required buffer

Have a plumbing expert help

As you can see, figuring out dimensions and where different fixtures should go can be complicated. Oftentimes, a professional plumber can come in and help everything makes sense, and fit.

At Liberty Plumbing, we provide experienced plumbers to the Winchester and surrounding southern California areas. Call us today at (951) 760-4215.

We are honored to serve you and will show the utmost integrity while taking care of your needs.

You can depend on our highly trained, certified staff and know we have the ability to exceed your expectations.

CALL US NOW (951) 760-4215

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