Often the hardest part about plumbing is the rough-in. The last step of connecting the sink, toilet, or tub is almost superfluous. Get the rough-in right, and you are 90 percent of the way there. 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 them 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, 8 1/4 inches above the floor; cold-water-only pipe creates one hole between 5 and 10 inches above the floor
- Supply line (horizontal): Measured from centerline running vertically through the center of the toilet, supply line hole should be 6 inches to the side of centerline; check toilet to confirm 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 recommended if bathroom layout allows
- 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; one hole is 4 inches to the right of centerline; other is 4 inches to left of 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; where shower arm will go; showerhead will be about 65 to 78 inches above the floor
- Tub supply (vertical): Faucet valves 20 to 22 inches above the floor; horizontally, each faucet goes 4 inches to the right/left of centerline; tub spout 4 inches above tub 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
Source: The Spruce
