How to Install a Bathroom Vanity Cabinet

Installing a bathroom vanity cabinet is one of the most rewarding DIY bathroom upgrades. You get an immediate visual transformation, added storage, and a functional sink all in one afternoon. The work itself breaks into two distinct phases: the carpentry (getting the cabinet level and fastened to the wall studs) and the plumbing (connecting supply lines and drain). Neither is complex, but both demand precision. A vanity installed crooked or with loose plumbing connections will telegraph its problems for years. Done right, it anchors the entire bathroom and gives you the confidence to tackle bigger projects. Most homeowners can handle this without a contractor, though calling a plumber for the rough-in connections (if your bathroom is a blank slate) is worth considering.

1. Kill the Water First. Locate the main water shut-off valve in your basement or under the kitchen sink and turn it clockwise until it stops. If your bathroom has individual shut-off valves under the sink, use those instead. Open the faucet to release any remaining water pressure. Once water stops flowing, you have a dry workspace.
2. Extract the Old Cabinet. Disconnect the supply lines by turning the compression nuts counter-clockwise by hand or with a wrench. You'll see a small amount of water—have towels ready. Unscrew or loosen the P-trap under the sink (this is the curved pipe below the drain). Once plumbing is free, check underneath the vanity for fastening screws. Unscrew them, then carefully pull the cabinet away from the wall. You may need to tap it gently with a rubber mallet if it's caulked.
3. Find Your Studs. Use a stud finder to locate the vertical studs behind the wall. Mark them lightly with pencil. Position your new vanity cabinet against the wall where you want it to sit permanently. Mark the wall lightly at each corner of the cabinet. Check that the cabinet is level side to side and front to back using a 24-inch level. Adjust the cabinet position until both planes are true. Mark the mounting holes on the wall where they align with cabinet fastening points.
4. Drill Your Pilot Holes. Align the vanity cabinet with your marks and have a helper hold it in position, or use shims underneath to keep it stable at the correct height. Mark the center point of each mounting hole from the vanity mounting rails onto the wall. Move the cabinet aside and drill pilot holes at those marks using a drill bit slightly smaller than your mounting bolts. These holes guide the bolts and prevent splitting.
5. Anchor to the Studs. Position the vanity cabinet back against the wall, aligning the mounting holes with your pilot holes. Insert lag bolts or wood screws through the cabinet's mounting rails and into the studs. Tighten with a wrench or screwdriver, but don't over-tighten—you want snug contact, not deformed wood. Check level again after tightening the first two bolts, then complete the rest.
6. Connect the Supply Lines. Hand-tighten the hot and cold supply line compression nuts onto the faucet inlet ports (usually located on the underside of the faucet body). Use an adjustable wrench to tighten an additional quarter turn past hand-tight. Don't over-tighten or you'll damage the ferrule seal. Turn water back on at the shut-off valve slowly and check for drips at both connections. If water drips, tighten another quarter turn.
7. Install the P-Trap. Slide the P-trap onto the drain tailpiece coming down from the sink. Hand-tighten the slip nut where the P-trap connects to the tailpiece, then hand-tighten it to the wall drain stub. Use a pipe wrench to tighten each slip nut an additional quarter turn. The trap should hang at a slight angle downward toward the wall. Fill the sink and watch underneath—if water drips from a connection, tighten that nut a quarter turn more.
8. Test for Leaks. Fill the sink completely with hot and cold water. Let it sit for 30 seconds to check for slow leaks. Drain it and observe the P-trap and all connection points. Run water from both hot and cold for one full minute, then check again. If any connection weeps water, tighten the slip nut or compression nut a quarter turn and retest. Do not overtighten—this crushes ferrules and makes leaks worse.
9. Mount Hardware and Trim. Install drawer pulls and cabinet door handles according to manufacturer specifications—usually predrilled holes guide placement. If your vanity includes a pre-installed countertop, verify it's level. If you're installing a separate countertop or backsplash, use construction adhesive and fasteners recommended by the countertop manufacturer. Caulk the top edges where the countertop meets the wall using paintable silicone caulk.
10. Seal the Seams. Run a bead of paintable silicone caulk along the seams where the cabinet sides and top meet the wall. Smooth the caulk with a wet finger or caulk tool. This prevents water from running behind the cabinet during cleaning and adds a finished appearance. Let caulk cure according to the product instructions (usually 24 hours) before exposing it to water.
11. Install the Faucet. If your faucet came separately from the vanity, install the handles and spout according to the manufacturer's instructions. This varies widely, but typically involves inserting the spout through the countertop hole and securing it with a mounting nut underneath, then screwing handle bases onto the supply line inlets and inserting handle stems. Adjust handle height and spout reach if adjustment screws are provided. Verify handles move smoothly and that the spout clears the sink basin completely.