Vanity listings lead with a single number — 24, 30, 36, 48 inches — and that number is the least likely thing to go wrong. Three other measurements are what send vanities back.
Start with the wall run, not the vanity
Measure the full wall the vanity will sit against, then subtract anything that intrudes: a door casing, a radiator, the toilet's required side clearance. What is left is your usable run. A vanity that fits the wall but blocks the bathroom door is still the wrong vanity.
Why 36 inches is the workhorse width
At 36 in. you get usable counter on both sides of a single basin — somewhere to put a toothbrush, a soap dish, a folded towel — while still leaving floor space in a small bathroom. Below 30 in. the counter effectively disappears; above 48 in. you are usually better served by a double basin. For most single-bathroom homes, 36 in. is the point where the trade-off stops improving.
Door swing — the measurement people skip
Vanity doors swing out. So does the bathroom door. Measure the arc of both and check they do not meet. In a tight bathroom, drawers or a wall-mounted unit solve this where hinged doors cannot.
The drain and supply positions
Compare where your existing drain and supply lines come out of the wall or floor against the vanity's cut-out. A centred basin over a centred drain is a straight swap. An offset basin, or a wall-mounted unit over floor plumbing, means moving pipework — budget for a plumber before you decide the vanity is the cheaper option.
"With top" versus cabinet-only
Many vanity listings — including on the large retailers — are the cabinet only. The countertop and basin are a separate purchase that can add substantially to the price. Check this first when comparing two vanities that look similarly priced.
A concrete example
The 36 in. Modern Single-Sink Bathroom Vanity with Top Sink is the configuration this guide describes: 36 in. wide, single basin, and the top and sink are included rather than sold separately, with two soft-closing doors. It ships at our $39 flat delivery rate.
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