How to Measure for a 31-Inch Bathroom Vanity?

Measuring for a 31-inch bathroom vanity starts with your wall space, not the cabinet’s advertised label.

One wrong measurement and a 31-inch vanity turns into a 32-inch problem. The fix isn’t complicated: you need the usable wall width, the floor-to-counter height, the depth, and a clear picture of what’s around the cabinet—doors, drawers, plumbing, and toilet. The steps below walk through each check in the order that prevents the most expensive mistake: buying a vanity that doesn’t fit.

Start With The Wall Width, Not The Baseboard

Measure the wall where the vanity will sit, from the finished wall surface on one side to the other. Run the tape at the floor level and again at countertop height—old houses often have walls that bow, and you want the smaller of the two numbers. That smaller width is your true usable space.

Safety note: measure from the wall itself, not the baseboard. Baseboard molding sticks out further than the drywall, and measuring from it will leave you with a vanity that’s too wide. One more adjustment: subtract a small amount from your measured width—roughly a half-inch to an inch—for installation breathing room. A cabinet that’s exactly flush against both walls is nearly impossible to level and shim.

Here’s where the label gets tricky. A 31-inch model isn’t always 31 inches wide. Home Depot’s Glacier Bay 31-inch single-sink freestanding unit, for example, lists an actual cabinet width of 30.50 inches. The name is a category, not a precise spec—always confirm the product’s exact dimensions before buying.

The Height And Depth Numbers That Matter

Vanity height is more standardized than width. Home Depot’s measurement guide says most standard bathroom vanities run 31 to 32 inches high, though other guides list the range up to 36 inches. Measure your existing cabinet from the base to the top of the countertop, as Lowe’s recommends, to see what you’re replacing and what will feel comfortable.

Depth is the number people forget until the cabinet blocks the doorway. Standard depth runs 18 to 24 inches, with most common units around 21 to 22 inches. The Glacier Bay model above is 19 inches deep, and its countertop is 18.75 inches deep—a small but real difference. Check both numbers. A 24-inch-deep vanity in a narrow bathroom can eat your walking space fast.

If you’re replacing an existing vanity, measuring its height and depth gives you a baseline that already works in your bathroom. Match it or stay within an inch or two and you avoid most fit surprises.

Clearance Checks: Doors, Toilets, And Plumbing

Open the bathroom door and the shower door fully before you measure. Lowe’s calls this out specifically—a door that swings into the vanity’s space will strike the cabinet every time. The same logic applies inside the vanity itself: make sure cabinet doors and drawers can open fully without hitting a wall, a towel bar, or the toilet.

Plumbing location matters more than the vanity’s looks. Note where the drain centerline and water supply lines exit the wall before choosing a model. A 31-inch vanity with a centered drawer stack can block an off-center drain. Confirm the cabinet’s back panel has the cutouts or open space to accommodate your plumbing rough-in.

Toilet clearance is the other common miss. If the toilet shares the wall with the vanity, you need comfortable and code-compliant spacing. One source recommends at least 18 inches from the toilet center to the cabinet edge; another cites 15 inches as an NKBA recommendation. Verify your local code, but at minimum keep the toilet usable without your knees hitting the vanity’s corner.

Finally, walk the traffic path. Allow at least 30 inches of clear floor space in front of the vanity. Check that the cabinet won’t block outlets or light switches on adjacent walls.

Ready to see which models actually fit after you measure? Our roundup of the best 31-inch bathroom vanities compares real sizes, materials, and sink options side by side.

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