How to Build a Bathroom Cabinet | Studs, Leveling & Sealing

Building a bathroom cabinet requires anchoring a plywood box to wall studs, leveling it with shims, and sealing all joints against moisture.

For the full breakdown, see our best High Bathroom Cabinet Storage guide.

Whether you’re installing a pre-built vanity or constructing a cabinet from scratch, the workflow stays the same: measure the space and plumbing, assemble the box, cut openings for the pipes, and anchor everything to the wall framing. The difference between a cabinet that lasts a decade and one that fails in two years usually comes down to three things — finding the studs, getting it level, and sealing every seam. Here’s the order that works.

Measure and Plan the Cabinet Layout

Before any wood gets cut, measure the bathroom footprint and the plumbing location. The cabinet center needs to align with the wall plumbing so the supply lines and drain line up with the cutouts you’ll make in the back panel. Mark the pipe positions on the wall, then transfer those measurements to the cabinet carcass.

Also check the wall for studs at this stage. Studs in framed walls generally sit 12–16 inches apart, and you’ll need to know their exact positions before anchoring. A stud finder makes this quick — mark every stud location with a pencil line.

Cut Plumbing Openings

Once the cabinet parts are cut and the box is assembled, mark the exact pipe locations on the back panel and cut the openings with a jigsaw or hole saw. Measure from the pipe itself, not from the wall or floor, because plumbing is rarely perfectly straight. Cut openings slightly oversize — it’s easier to seal a small gap than to enlarge a too-small hole after the cabinet is mounted.

The most common mistake here is cutting openings in the wrong place because the measurement was taken before the cabinet was positioned against the wall. Position the cabinet in place first, mark the pipe locations from inside, then cut.

Level, Shim, and Anchor to Studs

Set the cabinet in position and check it with a level — both front-to-back and side-to-side. Bathroom floors are rarely perfectly flat, so shims under the cabinet base are normal and expected. Slide shims in until the cabinet reads level, then trim the excess.

For anchoring, cabinet installation guides specify driving screws through the cabinet back, through any shims, and into the wall studs. One major retailer’s install guide recommends 3-inch screws for this job. Place screws near the top and bottom of the cabinet at each stud location, with pilot holes drilled first to prevent the wood from splitting.

If no stud exists where you need to anchor — which happens with older walls or unusual layouts — molly screws or toggle bolts can hold the cabinet, though they won’t support as much weight as a solid stud connection. On tiled or finished walls, this is also the point where you’ll need to work carefully to avoid cracking the tile.

Install Countertop, Sink, and Seal Everything

After anchoring, set the countertop on the cabinet and mount the sink and faucet according to the manufacturers’ instructions. Reconnect the drain and supply lines only after the countertop is seated. One manufacturer’s guide notes that vanities and tops must be installed onto finished surfaces — meaning the wall and floor should be complete before the cabinet goes in.

Sealing is the step that separates a bathroom cabinet from a moisture-damaged one. Apply silicone or caulk along the countertop-to-wall joint and around backsplash seams to keep water from seeping behind the cabinet. Let the sealant cure for the full time specified on the tube — the Home Depot installation guide cites 24 hours — before using water in the area.

Bathroom cabinetry lives in a room full of steam and splashes, so the finish on the cabinet and the sealed joints matter as much as the structural work. Skip the sealant and you’re inviting swelling, warping, and mold growth in the panels that touch the wall.

FAQs

Do I need a licensed plumber to install a bathroom vanity?

Some manufacturer installation guides state that all vanities must be installed by a licensed plumber, particularly when the work involves connecting supply and drain lines. Local building codes vary, so check your municipality’s requirements. DIYers comfortable with basic plumbing can often handle the installation themselves, but a permit or professional inspection may still be required.

What size screws should I use to secure a bathroom cabinet to the wall?

One major retailer’s installation guide specifies 3-inch screws driven through the cabinet back and into wall studs. The screw must be long enough to pass through the cabinet back panel, any shims, and drywall, then bite at least an inch into the stud. Pilot holes prevent the cabinet wood from splitting during installation.

Can I mount a bathroom cabinet without hitting a wall stud?

If studs are not available in the cabinet area, molly screws or toggle bolts can be used instead, though they provide less holding strength than a screw anchored into a stud. For heavy cabinets or wall-mounted units, additional wall reinforcement may be necessary. Check the cabinet manufacturer’s specifications for weight limits.