How to measure a sink base cabinet

Every under-sink mat return starts the same way: someone bought a mat the size of their cabinet. A "36-inch cabinet" is 36 inches on the outside, where the tape measure never needs to go. Inside, after two 0.75-inch side panels, you have about 34.5 inches of floor. Buy a 36-inch-wide anything and it will lean against the walls like a bad shelf.

The good news: measuring the part that matters takes under a minute.

Measure the interior width

Open both doors and clear the cabinet floor. Run the tape across the flat interior floor from side wall to side wall, behind the face frame. That number, usually 22.25, 28.25, 31.25, or 34.5 inches for kitchen bases, is your cabinet's real size.

Depth matters less than width because sink cabinets are standardized: kitchen bases run about 22.25 inches of usable depth, bathroom vanities about 19.25. That is why kitchen mats are 22 inches deep and vanity mats 19.

Pipes are not a measurement problem

The P-trap, supply lines and disposal all land on top of the mat, not through it. The mat slides in around fixed plumbing and sits beneath it. You are covering the floor, not re-plumbing the sink. The only hardware that matters is anything bolted through the cabinet floor itself, which is rare.

Match the number to a mat

Once you have interior width, the conversion is a lookup: a 24-inch base takes a 22 × 22 mat, a 30-inch base takes 28 × 22, a 33-inch base takes 31 × 22, and a 36-inch base takes 34.25 × 22. Vanities: 30-inch takes 28 × 19 and 36-inch takes 34 × 19. Between sizes? Size down; the raised lip still contains whatever the plumbing does.

Or skip the chart: the Fit Finder takes your measurement and hands back the exact size, with the fit guarantee behind it either way.