Standard sink base cabinet sizes, decoded

American cabinetry runs on 3-inch increments, and sink bases cluster at four widths: 24, 30, 33 and 36 inches. Those are nominal numbers, the outside face width, and every one of them hides roughly an inch and a half of box construction.

Kitchen sink bases

A 36-inch sink base, the most common in post-1990 American kitchens, has about 34.5 inches of interior width and 22.25 inches of usable depth. A 33-inch base interiors at about 31.25 inches; a 30-inch at 28.25; a compact 24-inch at 22.25. Frameless (European) cabinets run slightly wider inside, framed cabinets slightly narrower, but the ranges hold.

Depth is the stable number. Standard kitchen base cabinets are 24 inches deep outside, which nets about 22.25 inches of flat interior floor once you subtract the back panel and face frame.

Bathroom vanities are shallower

Vanities are 21 inches deep outside, not 24, which nets roughly 19.25 inches of interior floor. This is the detail most "universal" mats ignore: a 22-inch-deep kitchen mat will not sit flat in a vanity. Vanity-specific sizes, 28 × 19 and 34 × 19, exist because the room is genuinely different.

The conversion chart

24-inch base → about 22.25 in interior → 22 × 22 mat. 30-inch base → 28.25 in → 28 × 22 mat. 33-inch base → 31.25 in → 31 × 22 mat. 36-inch base → 34.5 in → 34.25 × 22 mat. 30-inch vanity → 28.25 in → 28 × 19 mat. 36-inch vanity → 34.25 in → 34 × 19 mat.

If you know your cabinet's nominal size, each one has its own fit guide: 36-inch sink base, 33-inch, 30-inch, 24-inch, 36-inch vanity, 30-inch vanity. If you don't, the Fit Finder resolves it from one measurement.