Calculate inside drawer-box dimensions from the opening and the slide hardware reduction.
Cut list
Material estimate
Usage Tip
Check the exact clearance in your slide instructions; brands vary, and full extension depends on matching the box depth to the slide length.
box height = opening height − 1/2 in
box depth = cabinet depth − 1/2 in
Width is reduced by the slide allowance; height and depth lose a half inch for clearance.
The drawer box that is 1/16 in too wide
A drawer box is unforgiving. Build it a sixteenth too wide and the slides bind; build it too narrow and the drawer rattles. The single number that decides this is the slide clearance, and it changes with every slide type. This tool starts from your cabinet opening and your slide, then gives you the whole package: box width, height and depth, the bottom panel size, a cut list, and a material estimate.
Slide clearance: the number that matters
Side-mount slides sit between the drawer and the cabinet, so they need room on each side. Undermount slides tuck beneath the box and need only a small gap. Get this wrong and nothing else matters.
| Slide type | Clearance each side | Box width from opening |
|---|---|---|
| Side mount / ball bearing | 1/2 in | opening minus 1 in |
| Accuride | 1/2 in | opening minus 1 in |
| Undermount (typical) | about 3/16 in | opening minus ~3/8 in |
| Blum Tandem | manufacturer spec | cut to Blum chart |
| Soft close | same as base type | matches side or under |
Side-mount clearance is consistent at 1/2 in per side. Undermount and Blum systems are manufacturer specific — always confirm against the slide instructions, then enter that exact clearance in the calculator.
Undermount vs side mount
Side-mount slides are forgiving, cheaper, and easy to install, but they show on the sides and eat an inch of drawer width. Undermount slides are hidden, give a premium full-extension feel and soft close, but they demand precise box dimensions and a square box. Most mistakes come from using a side-mount clearance on an undermount slide, or vice versa.
Cabinet type
On a frameless (Euro) cabinet the opening is the inside of the box, so slides mount directly to the cabinet sides. On a face-frame cabinet the opening is the frame, and side-mount slides usually need rear spacers or brackets to reach the same plane as the frame. Measure the actual clear opening either way.
Material thickness
Drawer sides are commonly 1/2 in for most drawers, 5/8 in for a furniture feel, and 3/4 in for heavy or wide drawers. Bottoms are usually 1/4 in plywood set into a groove. The side thickness drives the inside dimensions and the cut list.
The drawer box parts
A basic box is five pieces: two sides, a front and a back, and a bottom panel. In the common method the sides run the full depth and the front and back fit between them, so the front and back length equals the inside width. The bottom sits in a 1/4 in groove on all four sides.
Bottom panel size
The bottom is captured in a groove, so it is slightly larger than the inside opening by twice the groove depth. For 1/2 in sides and a 1/4 in groove, a box that is 23 in wide outside has a 22 in inside and a 22-1/2 in bottom panel. The calculator works this out for both width and depth.
Common drawer dimensions
| Opening width | Box width (side mount) |
|---|---|
| 12 in | 11 in |
| 18 in | 17 in |
| 24 in | 23 in |
| 30 in | 29 in |
Drawer depth guide
Box depth is set by the slide length, and slides come in fixed 2 in steps. Choose the longest standard slide that fits with about an inch to spare.
| Cabinet depth | Slide / box depth |
|---|---|
| 12 in | 10 in |
| 15 in | 14 in |
| 18 in | 16 in |
| 21 in | 20 in |
| 24 in | 22 in |
Tips before you cut
1. Confirm your slide clearance from the actual instructions, not memory. 2. Measure the clear opening, not the cabinet outside. 3. Keep the box dead square or undermount slides will fight you. 4. Cut the bottom groove before assembly. 5. Build a test box from scrap for an unfamiliar slide.
Frequently asked questions
How much narrower than the opening should the drawer box be?
For standard side-mount and ball-bearing slides, 1 in total — 1/2 in each side. Undermount slides need much less, often around 3/8 in total, but always confirm the maker spec.
What size is the drawer bottom?
The inside dimensions plus twice the groove depth. With 1/2 in sides and a 1/4 in groove, a 23 in outside box gives a 22-1/2 in wide bottom.
How deep should the drawer box be?
Match it to the longest standard slide that fits the cabinet depth with about an inch of clearance. Slides come in 10, 12, 14, 16, 18, 20, 22 and 24 in lengths.
Can I use side-mount clearance for undermount slides?
No. That is the most common drawer mistake. Undermount slides need a much smaller side gap and a precise box width.
What thickness for drawer sides?
1/2 in is standard, 5/8 in for a furniture feel, 3/4 in for heavy or wide drawers. Bottoms are usually 1/4 in plywood.
Does cabinet type change the box size?
It changes how you mount the slides and whether you need spacers, but the box is always sized from the clear opening and the slide clearance.
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Dimensions are a starting point. Slide clearances vary by brand and model, especially for undermount systems; always confirm against the manufacturer instructions and cut a test box in scrap before committing your final material.