Roughed in plumbing for a bathroom vanity and got the drain height wrong once. Had to cut into the wall after the drywall was up. Now I measure three times.
Standard Heights
For most vanities, the drain rough-in sits 18 to 24 inches above the finished floor. Measured to the center of the drain outlet, not the top or bottom.
That range works for standard vanity heights of 30-36 inches. Counter height plus sink depth determines how much vertical space you have to work with.
Why It Varies
Undermount sinks sit below the counter, so the drain ends up lower. You need room for the sink bowl plus the drain assembly.
Vessel sinks perch on top of the counter. The drain is higher because the bowl is above the counter surface, not below it.
Wall-hung vanities often need higher drains because there’s no cabinet to hide low plumbing. Everything visible needs to look intentional.
The P-Trap Factor
The P-trap hangs below the drain. It needs to connect to the wall pipe with proper slope for drainage. Calculate backward from where your wall pipe exits to find where your drain centerline should be.
Typical P-trap depth is 6-8 inches below the drain hole. Make sure you have clearance.
Getting It Right
Know your exact vanity, sink, and counter before roughing in. Measure the finished heights and work backward. A tall counter with a deep undermount sink needs different plumbing than a low counter with a vessel sink.
When in doubt, go with the middle of the range and plan for some adjustability with your P-trap connections.
ADA Considerations
Accessible bathrooms have their own requirements. Counter max height is 34 inches, and there needs to be knee clearance underneath. This usually means a wall-hung sink and careful drain positioning to keep pipes out of the way.
Check current ADA guidelines if accessibility is required. The rules are specific.
Common Mistakes
Assuming all vanities are the same height. They’re not. Measure the one you’re actually installing.
Forgetting about the sink bowl depth. A 6-inch deep sink is different from a 3-inch deep vessel bowl.
Ignoring the finished floor height. If tile or flooring comes after plumbing rough-in, account for that thickness.
Tools to Have
- Measuring tape – obvious but critical
- Level – drains need proper slope
- Pipe wrench and adjustable pliers
- Plumber’s tape for threaded connections
- PVC primer and cement if using plastic pipe
My Recommendation
Measure the actual fixtures before roughing in. If you haven’t bought them yet, wait until you have specs in hand. Changing rough-in heights after the wall is closed is expensive and frustrating.
Twenty minutes of careful planning saves hours of corrective work later.
