Drawer box calculator
Pick the drawer slide, then give the cabinet opening, its inside depth and your drawer side thickness. You get the drawer box's outside and inside width, its length and how tall it can be, worked from that slide maker's own installation figures.
One source: Knape & Vogt, the maker of the 8400 slide
Drawer box, outside width
20 in
Inside: 19 in
- Box length
- 22 in
- Slide length
- 22 in
- Side height, at least
- 1.79 in
Knape & Vogt gives no height clearance for the 8400: the box can be as tall as the opening allows, with sides at least as tall as the slide.
Why: Knape & Vogt asks for 1/2 in each side of the 8400, so a 21 in opening takes a 20 in box on a 22 in slide.
Why these numbers?
The situation
An opening 21 in wide and 6 in high, 22 in deep inside, with 1/2 in drawer sides.
From your input: the opening, the cabinet depth and the side thickness
What that means
The 8400 needs 1/2 in between the drawer and the cabinet on each side; it comes in 8–28 in lengths and is 1.79 in tall.
One source: Knape & Vogt, the maker of the 8400 slide , sources [1]
So
21 − 2 × 1/2 = 20 in outside; less two 1/2 in sides = 19 in inside.
Arithmetic: exact by definition
The number
The longest slide that fits 22 in is 22 in, and the box is as long as its slide. The drawer side must be at least 1.79 in tall to carry it.
Arithmetic: exact by definition
Sources
How a drawer box is sized for its slides
Side-mount slides live in the gap between the drawer and the cabinet, so the box is the opening less that gap on both sides. The gap is each slide's own: Knape & Vogt asks for 1/2 inch each side of its 8400 and 3/4 inch for the heavier 8800. That is why the calculator never averages across slides; a box built for one will not run on the other. The box is as long as the longest slide that fits the cabinet, and its sides must be at least as tall as the slide.
Undermount runners such as Blum's TANDEM sit under the drawer, hidden. Blum sizes the drawer from the opening: the inside width is the opening less 1-21/32 inches, and the outside width is the opening less a deduction that depends on the side thickness, 13/32 inch for 5/8 inch sides. The drawer is as long as the runner, and the cabinet needs a little more depth than the runner, which the calculator checks. The box can be at most the opening height less 25/32 inch.
A center-mount slide runs under the middle of the drawer, so it sets the box length and the room under the box but not the side gap, which is yours to choose. Knape & Vogt's 1175 is 22-5/8 inches long and rated for drawers up to 18 inches wide.
Every slide's figures are in the drawer slide sizes chart. For the overall size of the cabinet itself, see furniture dimensions.