Tool
Drawer box size calculator: from cabinet opening to the box you order
For anyone with the cabinet opening measured who needs the exact outside box size, in fractions to the 1/32 inch. Pick your mounting and, for undermount, your exact slide model, enter what you measured, and the calculator applies the same deduction rules our measuring guide and configurator already publish, then hands you a link that fills in the box for you.
Quick answer. A drawer box is sized from the clear cabinet opening: side mount boxes are the opening minus 1 in wide, undermount boxes follow the slide maker’s inside width rule (42 mm for Blum and most others, so 13/32 in narrower with 5/8 in sides), height is the opening minus the maker’s clearance, and depth equals the slide length. Enter your numbers below for the exact size.
What to measure
Three numbers feed the calculator. A is the clear opening width, inside edge to inside edge, read at the top, middle and bottom and kept at the smallest. B is the clear opening height, cabinet floor or the lower rail to the underside of the rail above. C is the inside cabinet depth, front edge to the back panel, and it is optional; skip it and the calculator still sizes the width and height, and lists the depths your slide comes in. All three are the opening, not an old box; if you still have the old box, measure it directly and skip to the configurator.
The full picture, with photos for each measurement, is in how to measure. Not sure what slide you have or whether your opening is even a custom size? Find my drawer asks three questions and points you to the right page first.
How the width rule works
Every slide maker publishes an inside width: how much room the drawer needs between its own two sides for the runner to work. Our shop builds to the outside width you order, so the calculator subtracts your side thickness twice, once per side, to land on that outside size. That is why thicker sides narrow an undermount box: the inside width is fixed by the runner, so a thicker side eats into the same space.
Side mount works differently. The slide clamps to the outside face of the side, not the inside, so its deduction, 1 in total, is fixed no matter how thick the sides are, the one rule here that never changes with side thickness.
Most undermount makers publish the same inside width, 42 mm, 13/32 in narrower with our standard 5/8 in sides. Würth prints the identical 10 mm deduction as 3/8 in instead, its own rounding of the same metric figure, so the tool shows the millimeters next to the inch figure for Würth models.
Height and depth
Height is the tallest box that fits; order it or anything shorter, since a shorter box only adds clearance. The calculator rounds down to the 1/32 inch and caps the fraction at 3/4 in, since the configurator’s Height Fraction list stops there. Each maker sets its own clearance: our side mount rule is commonly about 3/4 in under the rail, Blum 563 wants 13/16 in, Blum MOVENTO wants 29/32 in, Salice Futura Smove a full inch, and Hettich and most Würth PRO runners share a 13/16 in rule. Grass publishes no height rule for Dynapro, only a 7 mm (9/32 in) minimum clearance, so the calculator shows that instead of a number.
Depth works differently by mounting. On side and bottom mount, depth is whatever slide length you buy, so the calculator suggests the longest even length, 10 to 24 in, that leaves about 1 in behind the box, because side mount slides come in even lengths. On undermount, the runner only comes in set lengths, 9 up to 30 in by model, so the calculator picks the longest one whose minimum cabinet depth still fits what you measured. A few models, including Würth PRO634 and PRO600 Heavy Duty, have no minimum depth table in our sources; for those it lists the lengths on offer and asks you to confirm the fit against the runner.
Face frame cabinets
A face frame changes the hardware, not the box size. On undermount, the runner’s back end needs a rear mounting bracket to hang level with the frame instead of screwing to a flat cabinet side; the undermount drawer slide guide covers the bracket by brand. On side mount, the frame stile usually sits proud of the cabinet side, so the slide gets packed out flush with it using spacers, sized in the spacer guide and sold as drawer slide spacers. Pick Face frame in the calculator for the right note; frameless cabinets need neither.
When to use the quote instead
The calculator covers every mounting and slide our configurator builds for, within the sizes we cut: width 6 to 35 31/32 in, height 2 to 12 3/4 in, depth 9 to 24 31/32 in on a plain box or the runner’s own lengths to 30 in when notched. Outside that range, the tool points you to the instant quote instead of guessing. Same for a slide with no confirmed width rule: send the opening, the model and a photo, and we check it by hand.
What to pick in the configurator
The result links straight to the custom drawer box with your numbers filled in, but here is where each lands by hand. Side or bottom mount: leave “Notching” at “None,” then set “Width (Inches)” and “Width Fraction,” “Height (Inches)” and “Height Fraction,” “Custom Depth (Inches)” and “Depth Fraction.” Undermount: set “Notching” to “Notched & Drilled For Undermount Slides,” pick your runner under “Slide Brand/Model,” choose “Depth Selection,” and pick “Clips” if wanted. “Drawer Side Thickness” is the same field either way: “5/8" Thick Drawer Sides (Our Standard),” “1/2" Thick Drawer Sides (Thin)” or “3/4" Thick Drawer Sides (Thick).”
Decimals, fractions and the 1/32 in cut
Type your measurements however your tape reads them: a mixed fraction with a space, “22 1/2,” one with a hyphen, “22-1/2,” or a decimal, “22.5.” Every result comes back the way the configurator asks for it, a whole number plus a fraction in 1/32 in steps, such as “21 7/16 in.” Width and height round down, since a box a hair narrower or shorter still fits; a minimum cabinet depth rounds up instead, since reading short would say a cabinet fits when it does not.
Drawer box size questions
How do I calculate drawer box size from the cabinet opening?
Measure the clear opening, then subtract your slide’s own deduction: 1 in off the width for side mount, or the slide maker’s inside width rule for undermount, commonly 42 mm, 13/32 in narrower with 5/8 in sides. This calculator does that subtraction and rounds to the 1/32 in the configurator expects.
How much smaller than the opening should a drawer box be?
1 in narrower on side mount, 1/2 in per side. Undermount sits much closer to the full opening: 13/32 in narrower with our standard 5/8 in sides on most named brands, since the runner sits under the box rather than beside it.
Does side thickness change the box width?
Only on undermount, where a thicker side eats into the runner’s fixed inside width and narrows the outside box. Side mount is unaffected: the slide clamps to the outside face of the side, so the 1 in deduction never changes.
How tall can a drawer box be for undermount slides?
The opening height minus the maker’s own clearance: 13/16 in for Blum 563, Hettich Quadro V6 and most Würth PRO runners, 29/32 in for Blum MOVENTO, a full inch for Salice Futura Smove. Grass publishes only a 7 mm minimum clearance for Dynapro, not a height rule, so measure your own runner for that one.
How deep should a drawer box be?
Exactly as deep as the slide. On side and bottom mount, pick the longest even length, 10 to 24 in, that leaves about 1 in behind the box, because side mount slides come in even lengths. On undermount, depth is the longest length on that model’s list whose published minimum cabinet depth still fits what you measured.
Why does the calculator not give a width for some slides?
A few combinations have no confirmed width rule: our sources hold no width figure for Würth PRO634 at any side thickness, and most models have no confirmed figure at 3/4 in sides. Rather than guess, the calculator says we confirm the width against the maker’s drawing when you order, and leaves width out of the generated link.
Can I order a box shorter than the calculated height?
Yes. The calculated height is the tallest the opening and the slide allow, not a fixed target, so anything shorter still clears the rail with room to spare. Order it for the most drawer space, or a shorter one on purpose, such as matching a stack above or below it.
What if my opening is out of square?
Measure the width at the top, middle and bottom, and the height at both sides, then use the smallest reading in the calculator. A box built to the larger reading can bind in the tighter spot; one built to the smallest still fits everywhere.
Related reading
- How to measure: every measurement with photos and a printable worksheet.
- Find my drawer: three questions that sort standard from custom and side mount from undermount.
- Undermount drawer slide guide: the width rule, notch and clip for every runner.
- Side mount drawer slides explained: the side mount width rule in detail.
- Undermount drawer slides explained: how the notch, hook and clip work together.
- Bottom mount drawer slides explained: epoxy roller slides and what changes.
- Drawer box sizes: every standard size, and when one fits your opening.
Put this calculator on your own site
Cabinet shops and bloggers are welcome to embed this calculator on their own site, free, with a line of code.
Ready to build it?
Enter your opening above and the calculator hands you a link with the exact width, height and depth already filled in. We build the box to order in our Las Vegas shop, cut to the 1/32 inch, with a lifetime warranty on the wood box. Plain custom boxes start at $46.99. Rather send us your numbers directly? The instant quote takes your measurements and a photo.