Rough-In Plumbing Dimensions for the Bathroom

Bathroom plumbing pipes

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Often the hardest part about plumbing is the rough-in. The last step of connecting the sink, toilet, or tub can sometimes feel superfluous. If you get the rough-in right, you are 90 percent of the way toward project completion.

But it doesn't have to seem so daunting. There are generally accepted plumbing rough-in measurements for sinks, toilets, and tub/showers. In addition, fixture manufacturers typically provide rough-in specifications in their product literature. Always check the standard dimensions against the manufacturer's specs to make sure they will work for your installation.

Rough-In Dimension Terminology

When speaking of plumbing dimensions, the term centerline is often used. As with the term "on-center," which is used for construction, the term "centerline" is an imaginary vertical line drawn through a key reference point (usually the drain pipe). For example, if two pipes are specified to be 10 inches apart, you measure 10 inches between the centers of the pipes, not 10 inches between the edges of the pipes.

Another common term is the base floor height. This is considered to be the subfloor (in new construction) or the finish flooring (in remodeling).

Keep in mind that not all dimensions are set in stone; consider these dimensions to be general guidelines. They will vary according to your bathroom. Consult the instructions that come with the fixture (sink, tub, etc.) for 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

Toilet Rough-In Details

  • Supply line (height): Ideally, the toilet's water supply line enters the room at 8 1/4 inches above the floor. More broadly, this cold-water-only pipe creates one hole between 5 and 10 inches above the floor.
  • Supply line (horizontal): Horizontally, the water supply line is measured from the centerline running vertically through the center of the toilet. The water supply line hole should be 6 inches to the side of the centerline. Check the toilet to confirm the location water supply connection.
  • Discharge hole from back wall: Offset hole from the back wall by 12 1/2 inches.
  • Discharge hole (vertical): Drain located at floor height; distance is zero.
  • Fixture (side to side buffer): Measured from center of the toilet to either side, minimum. clearance is 15 inches to any wall or other fixture; 18 inches is recommended if the bathroom layout allows for this.
  • Fixture (front buffer): Measured from the front rim of toilet forward, minimum clearance is 21 inches to the nearest obstruction; 30 inches recommended.

Sink Rough-In Details

  • Supply line (height): Two holes; vertically, both are about 2 to 3 inches above the drain pipe.
  • Supply lines (horizontal): Two holes are required, one for the hot water supply and the other for the cold water supply. One hole is 4 inches to the right of the centerline and the other is 4 inches to the left of the centerline.
  • Discharge hole (vertical): About 16 to 20 inches above the floor; consider 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 Rough-In Details

  • Shower supply (vertical): 80 inches from the floor is where the shower arm will be located. The 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 4 inches to the right/left of the centerline and the tub spout 4 inches above the tub rim.
  • Discharge hole from back wall: Place drain on the centerline. The 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.