Drawer Slide Calculator

An undermount slide sits below the drawer box and grips a groove or bracket on the bottom, so it doesn't consume space on the sides at all beyond a small 3/16 inch gap per side. But because the slide mechanism and its face-frame mounting bracket sit underneath and behind the drawer, the calculator subtracts 0.75 inch of total height instead of the 1 inch used for full-extension and center-mount, which need top-and-bottom running clearance along the sides instead.

It walks the standard commercial slide lengths (12, 14, 16, 18, 20, 22, and 24 inches) and keeps the largest one that still fits inside your calculated drawer depth, so the slide never protrudes past the back of the cabinet. If your cabinet depth is shallow enough that even the 12-inch slide doesn't fit the pattern, the calculator still returns 12 inches as the smallest standard option rather than a custom length.

Interior Usable Height subtracts an additional half inch from the drawer box height to account for a 1/4-inch plywood bottom panel sitting in a dado groove near the base of the sides. That half inch isn't wasted — it's the physical thickness and groove depth the bottom panel occupies — so it tells you how much clear space is actually available for whatever you're storing inside the finished drawer.

Since each slide type carries a different clearance-per-side and height-clearance value baked into the formula, selecting full-extension when you actually have undermount hardware (or vice versa) will size the drawer box incorrectly — typically too narrow or too loose for the slides you're actually installing. Always match the Slide Type selector to the physical hardware package before cutting stock, since the calculator has no way to detect a mismatch on its own.