The old vanity has been an eyesore since you bought the house. The cabinet doors do not close square. The laminate countertop is peeling at the edges. The sink has a hairline crack radiating out from the drain that you have been monitoring for two years. You bought a new vanity. It is sitting in its cardboard box in the hallway. The box is slightly too wide to walk around comfortably, which adds a daily reminder that the project needs to happen.
Installing a bathroom vanity is a plumbing project and a carpentry project in roughly equal measure. The plumbing involves disconnecting and reconnecting two water supply lines and a drain. The carpentry involves leveling a cabinet on a bathroom floor that is almost certainly not level, securing it to wall studs that are almost certainly not where you need them, and cutting holes in the back of the cabinet to accommodate plumbing that is almost certainly not at the exact height and position the vanity expects. This guide covers the full sequence, including the parts that the vanity instruction sheet assumes your bathroom already matches.
Before You Buy: The Rough-In Measurements
The most common mistake in vanity installation happens before the old vanity is removed. It is buying a new vanity that does not fit the plumbing rough-in. The drain pipe and water supply lines come out of the wall or the floor at specific positions. The new vanity must accommodate those positions or the plumbing must be moved. Moving plumbing inside a finished wall is not a vanity installation project. It is a plumbing rough-in project that requires opening the wall.
Measure the distance from the floor to the center of the drain pipe coming out of the wall. Measure the distance between the hot and cold supply valves. Measure the height of the supply valves above the floor. Open the new vanity cabinet doors and compare these measurements to the interior layout. The drain pipe must pass through the back of the vanity or through the bottom shelf without interfering with drawers, shelves, or the cabinet frame. If the vanity has drawers, confirm that the top drawer closes without hitting the plumbing. Many a vanity installation has been completed only to discover that the top drawer is permanently open because the drain trap occupies the same physical space.
Step 1: Remove the Old Vanity
Turn off the water supply valves under the sink. If there are no individual shutoff valves, turn off the main water supply. Disconnect the water supply lines from the shutoff valves. Place a small bowl under each connection to catch the water in the lines.
Disconnect the P-trap under the sink. The P-trap is the U-shaped pipe that connects the sink drain to the wall pipe. Place a bucket underneath. Unscrew the slip nuts by hand. Water in the trap will spill out. It will smell. This is normal. The trap holds water to block sewer gases, and that water has been sitting there since the last time the sink was used.
Cut the caulk seal between the vanity backsplash and the wall with a utility knife. If the vanity is screwed to the wall, which it should be, remove the screws through the back rail inside the cabinet. The old vanity is now free. Rock it away from the wall and carry it out. The floor underneath will be a different color than the rest of the bathroom, and there will be a gap in the baseboard where the vanity was. The new vanity will cover this.
Step 2: Prepare the Wall and Floor
Locate the wall studs behind where the vanity will sit. Use a stud finder or measure 16 inches from a known stud location such as an electrical outlet box. Mark the stud centers with painter’s tape above where the vanity will sit, not on the drywall where the mark will be hidden once the vanity is in place.
The new vanity must be screwed into at least two wall studs. A vanity that is not secured to the wall will shift when someone leans on the countertop, which breaks the caulk seal at the backsplash and allows water behind the vanity. If the studs do not align with the vanity’s back rail, which is common, install a horizontal 1×4 cleat between the studs inside the wall. Cut a section of drywall behind where the vanity will sit, screw the cleat to the studs, and patch the drywall. The vanity covers the patch. The cleat provides a solid mounting point anywhere along the back of the vanity.
Check the floor for level where the vanity will sit. Most bathroom floors slope slightly toward the drain. A 1/4-inch slope over the width of a vanity is enough to make the cabinet doors hang crooked and the countertop sit out of level. Slide shims under the low side of the vanity base until it is level both front-to-back and side-to-side. Use a 2-foot level. Shim at the points where the vanity contacts the floor. Do not shim the entire perimeter. The shims transfer weight to the floor. Air gaps squeak.
Step 3: Cut Plumbing Access Holes
Measure the positions of the water supply lines and drain pipe relative to the back or bottom of the vanity. Transfer these measurements to the vanity cabinet. Drill access holes using a hole saw or a spade bit. The holes should be 1/2 inch larger in diameter than the pipe they accommodate. This clearance allows for slight misalignment and prevents the cabinet from contacting the pipes, which would transmit vibration and noise.
If the vanity has a solid back panel, the holes go through the back. If the vanity has an open back, the plumbing passes through the bottom shelf. If the plumbing comes through the floor rather than the wall, the holes go through the bottom of the cabinet. Cut from the inside of the cabinet outward to minimize tear-out on the finished exterior surface.
Step 4: Set and Level the Vanity
Slide the vanity into position over the plumbing. The pipes should pass through the access holes without forcing. If a pipe binds against the cabinet, enlarge the hole. Do not notch the cabinet frame to clear a pipe. The frame carries the countertop weight. Notching it weakens the structure.
Level the vanity using shims. Check level in both directions. Check that the cabinet doors and drawers open and close smoothly. A cabinet that is twisted slightly out of square will have doors that swing open on their own or drawers that bind against the frame. Adjust the shims until everything operates correctly. Drive screws through the back rail of the vanity into the wall studs or into the cleat you installed. Use at least two screws per stud. The screws should be long enough to penetrate 1-1/2 inches into the framing. Standard 2-1/2-inch wood screws work for most installations.
Trim the visible portions of the shims flush with the vanity base using a utility knife. Score the shim deeply and snap it off. Install the toe kick if the vanity has a separate toe kick board.
Step 5: Install the Countertop and Sink
Most vanities come with a pre-attached countertop and sink. If the vanity and countertop are separate, set the countertop on the vanity base. Apply a bead of silicone caulk along the top edge of the vanity before setting the countertop. The caulk prevents water from seeping between the countertop and the cabinet. Center the countertop so the overhang is equal on both sides and the front.
If the sink is separate from the countertop, apply a bead of plumber’s putty or silicone under the sink rim and press it into the countertop opening. Secure it with the clips and screws provided with the sink. Wipe away excess putty or caulk immediately. Once it dries, removing it without scratching the countertop is difficult.
Step 6: Reconnect the Plumbing
Install the faucet on the sink or countertop before the vanity is pushed fully against the wall if access to the underside of the faucet is tight. Faucets are easier to install on a countertop resting on sawhorses than on a countertop already mounted in a cabinet. Feed the faucet supply lines and the mounting studs through the holes in the sink or countertop. Tighten the mounting nuts from underneath.
Connect the water supply lines from the shutoff valves to the faucet inlets. Hand-tighten, then a quarter turn with a wrench. Connect the P-trap to the sink drain and the wall pipe. The trap arm slides into the wall pipe and is sealed by a slip nut and a plastic compression washer. The washer is tapered. The tapered side faces the nut so it compresses against the pipe as the nut is tightened. Installing the washer backward is a common mistake that produces a slow drip at the wall connection.
Turn the water on slowly. Watch each connection as the water flows for the first time. Dry paper towels under each joint reveal a seep that is invisible to the eye. Check the drain by filling the sink halfway, then pulling the stopper. The full volume of water draining at once is the highest-pressure test the drain connections will face. If the joints are dry during a full-sink drain, they will stay dry under normal use.
Step 7: Caulk and Finish
Apply a bead of silicone caulk along the joint between the backsplash and the wall. Apply a bead along the joint between the countertop and the backsplash if they are separate pieces. Do not caulk the gap between the vanity base and the floor. That gap allows any water that reaches the floor under the vanity to evaporate rather than being trapped behind a caulk bead.
Reinstall the baseboard around the vanity if it was removed. Install any cabinet hardware such as knobs or pulls. Adjust the cabinet doors using the adjustment screws on the hinges if they are not perfectly aligned after leveling.
What Installing a Bathroom Vanity Costs
| Item | DIY Cost | Pro Cost (Installed) |
| Vanity with countertop and sink | $200-800 | $200-800 |
| Faucet (if not included) | $50-150 | $50-150 |
| Supply lines, P-trap, caulk, shims | $20-40 | Included |
| Labor | $0 | $300-700 |
| Plumbing rough-in modification (if needed) | Not DIY | $200-500 |
| Total (straightforward replacement) | $270-990 | $550-1,650 |
Frequently Asked Questions
How do I know if the top drawer will clear the plumbing before I buy the vanity?
Measure the depth of the top drawer when closed, which is the distance from the back of the drawer to the back of the cabinet. Measure the distance from the front of the cabinet to the center of the drain pipe when the vanity is in position. If the drain pipe falls within the drawer’s travel path, the drawer will not close. Look for a vanity with a shallower top drawer, typically called a “tipped drawer” or “U-shaped drawer” that is notched around the plumbing. These are designed specifically for bathroom installations. Standard flat-front drawers that extend the full depth of the cabinet will interfere with the drain.
The vanity covers a floor HVAC register. What do I do?
Do not cover an active HVAC register with a vanity. The restricted airflow reduces heating and cooling efficiency, and the humidity from the vanity location can cause condensation inside the duct. Relocate the register or choose a vanity with legs that allows airflow underneath. A toe kick duct adapter can redirect the airflow out the front of the toe kick. The adapter costs $15 to $25 and installs between the duct and the toe kick opening.
Should I replace a vanity with a pedestal sink instead?
A pedestal sink saves floor space and makes a small bathroom feel larger, but it eliminates all storage. There is no cabinet. The plumbing is exposed and must be finished nicely because it is visible. Pedestal sinks also require the plumbing rough-in to be at specific heights because there is no cabinet to hide misaligned pipes. If the bathroom is the only one serving a bedroom and you need storage for toiletries and cleaning supplies, keep a vanity. If the bathroom is a powder room used only by guests, a pedestal sink is a better aesthetic choice.
The Vanity That Looks Like It Was Always There
A new bathroom vanity transforms the room more than any other single fixture. The old peeling laminate and the crooked doors are gone. The new cabinet is level, the drawers close smoothly, and the countertop is clean and undamaged. The plumbing reconnects the same way it disconnected. The only difficult part is the stud location and the drawer clearance. Both are resolved with measurements taken before the old vanity comes out.
Keep the old shutoff valves accessible. If a valve fails in the future, you need to be able to reach it without removing the vanity. The access holes in the back of the cabinet provide that access. Do not bury shutoff valves behind a solid cabinet back. The day will come when you need to turn them, and reaching them should not require tools.
Last modified: June 17, 2026
