Sizing a drawer box for side-mount slides

Work out drawer box width, height and length from the opening and the slide, including the half-inch side clearance for ball-bearing slides and inset or overlay fronts.

A drawer box is sized from two things: the opening it goes into and the hardware it runs on. Get either wrong and the drawer binds, sags, or falls off its slides. Side-mount ball-bearing slides are the most common hardware in home shops, and they are also the least forgiving, so they are a good place to start.

Measure the opening

Build the case or frame first, then measure the actual opening:

Width between the surfaces the slides mount to, at the front and at the back. If they differ, the case is out of square or the sides bow; fix that first or shim the slides.
Height of the opening.
Depth from the front edge of the opening to the back, inside the case.

Sizing drawers from the drawing rather than the built case is how small errors in the carcass become drawers that do not fit.

Width: side-mount slides need exact clearance

Ball-bearing side-mount slides fit in a gap between the drawer box and the cabinet side. For common full-extension slides, that gap is 1/2 inch per side. Accuride, for example, specifies 1/2 inch plus up to 1/32 inch per side for its 3832 series.

drawer box width = opening width − 1”

The tolerance is small. A box even 1/32 inch too wide can make the slides stiff; a box more than about 1/16 inch too narrow can let a slide disengage. Always check the specification sheet for the slide you are using, since some models differ.

If you are unsure of your accuracy, make the box a hair narrow rather than wide. A thin shim behind a slide can take up a small gap; a box that is too wide has to be rebuilt or trimmed.

Height

Side-mount slides do not need much vertical clearance, but the drawer needs room to be installed and to clear the case above it. A box about 1 inch shorter than the opening is a common starting point, with the slide mounted near the vertical centre of the box side or at a consistent height across a bank of drawers.

Length

Slides come in whole-inch lengths, typically in 2-inch steps. Choose the longest slide that fits the inside depth of the case, allowing for anything at the back, such as a back panel set into a rabbet. Then make the box the same length as the slide.

For inset drawers, remember the drawer front’s thickness sits inside the opening, and deduct it when checking whether a slide length fits.

Fronts: inset or overlay

Inset fronts sit inside the opening, flush with the face. They need a consistent gap all around, commonly about 1/16 inch, so they do not rub when the case moves with the seasons.
Overlay fronts cover the opening. Size them to overlap the frame or case by a consistent amount, commonly 3/8 to 1/2 inch per side for a full overlay on a face frame. Attach the front to the box after the box is installed, so you can adjust its position.

Box construction

A drawer box is four sides and a bottom:

Sides of 1/2- to 5/8-inch stock are typical for side-mount slides.
Bottom of 1/4-inch plywood in a groove about 1/4 inch deep, set 1/4 to 1/2 inch up from the bottom edge. Measure the plywood; “1/4-inch” plywood is usually thinner. See dadoes and rabbets in plywood.
Corners can be rabbets or dadoes, box joints, dovetails or simple butt joints with screws for utility drawers.

A worked example

Opening 15-1/2 inches wide, 5-1/2 inches high, and 19 inches deep inside the case, with 18-inch side-mount slides and 1/2-inch sides:

Box width: 15-1/2 − 1 = 14-1/2 inches outside.
Inside width: 14-1/2 − 2 × 1/2 = 13-1/2 inches.
Box height: about 4-1/2 inches.
Box length: 18 inches, to match the slides.
Bottom: 13-1/2 inches plus the two groove depths wide, sized from the grooves as cut.

Undermount slides

Undermount slides hide beneath the drawer and each manufacturer specifies the box: side thickness, the distance from the inside of the sides to the opening, how far the bottom is recessed, and notches or holes at the back. Follow the maker’s drawing exactly; the side-mount formula above does not apply.

In GrainDraft

Drawer boxes can be driven by formulas in GrainDraft: name the opening width and height, and set the box width to the opening minus the slide clearance. When the case changes size, the Dimensions preview lists the parts and joints that will change before you apply it. The side-table walkthrough follows a formula-driven frame and drawer from dimensions to shop files.

Numbers here are starting points from common shop practice and published references. Check your own stock, tools and hardware instructions, and cut a test piece before committing project wood. Spotted an error? The contact address is on the About page.