Drawer Box Calculator

Drawer Box Calculator for side-mount and Blum undermount slides. Enter the cabinet opening and side thickness to get the outside box size, its cut list and the slide length to buy.

Sizing Boxes With the Drawer Box Calculator

The Drawer Box Calculator starts from the cabinet opening, not from an old drawer. Measure between the face frame stiles and rails, or between the cabinet sides on a frameless box, then pick the slides you plan to buy.

From there it works out the outside box size, the part lengths for your corner joint, the bottom panel and the longest slide the cabinet can take. It suits kitchen remodelers, cabinet shops and anyone ordering or building replacement drawer boxes in inches or millimeters.

Side thickness is the measured size of your stock, not what the sheet is sold as. Blum tells builders to caliper drawer side material for exactly this reason, and the math below shows where a small thickness error ends up.

Side-Mount Width Is Opening Minus 1-1/16 in

Ball-bearing side-mount slides are 1/2 in thick, which is where the common rule of subtracting 1 in comes from. Kreg's drawer sizing guide uses that 1 in figure as a rule of thumb.

The Accuride 3832EC sheet is tighter. It calls for 1/2 in of side space plus up to 1/32 in on each side, warns that slides may not run if the space drops below 1/2 in, and says to build the box 1-1/16 in narrower than the opening.

$$W_{box}=W_{open}-1.0625$$

An 18 in opening gives a 16 15/16 in box with 17/32 in per side. A box built at 17 in sits right on the minimum, so a side that bows or a joint that grows even 1/32 in leaves less than the 1/2 in Accuride calls for.

Height is the opening minus your total vertical gap, 1 in by default. Kreg's guide says to take at least 1/2 in off the height, and the Accuride 3832EC installation sheet sets a minimum drawer height of 1-7/8 in for the slide itself.

The same sheet says the box should never be wider than the slide is long. Accuride also rates the 3832EC at 100 lb for drawers up to 24 in wide, and the results flag either limit when you pass it.

Picking the Slide Length From Cabinet Depth

Accuride sells the 3832EC in 2 in steps from 12 to 28 in, but each slide is a little shorter than its name. A 22 in slide measures 21.65 in, so it fits a 22 1/2 in deep cabinet with room to spare, while the 24 in slide at 23.62 in does not.

The box is built to the nominal slide length, so the default gives a 22 in long box. Kreg's guide says the same thing in plain terms, with drawer sides the same length as the slide.

Inset fronts change the answer. Accuride sets the slide back by the front thickness plus 1/8 in, so a 3/4 in inset front needs 21.65 + 0.75 + 0.125 = 22.525 in of depth for the 22 in slide.

That is 1/40 in more than the 22 1/2 in cabinet has. The inset version of the same drawer drops to the 20 in slide, which is worth knowing before you order a case of 22s.

Blum TANDEM and MOVENTO Fix the Inside Width

Undermount runners ride under the drawer sides, so Blum sizes the box from the inside. The TANDEM 563H instructions say the inside drawer width must equal the opening width minus 42 mm, which is 1-21/32 in.

$$W_{in}=W_{open}-42\text{mm}$$

The outside width then adds your real side thickness twice. An 18 in opening gives a 16 11/32 in inside width, so 1/2 in sides make a 17 11/32 in box and 5/8 in sides make it 17 19/32 in.

$$W_{box}=W_{in}+2t$$

Blum limits the sides to 16 mm (5/8 in) and the inside width to at least 170 mm, so the opening must be at least 212 mm (8-11/32 in). Box height is the opening minus 20 mm (25/32 in) for TANDEM and minus 23 mm (29/32 in) for MOVENTO, per the MOVENTO catalog.

The bottom sits in a groove 13 mm (1/2 in) up from the side's lower edge, so a nailed-on bottom is not offered with these runners. The back needs a rear notch at each corner, 35 mm (1-3/8 in) wide for TANDEM and 50 mm (1-15/16 in) for MOVENTO, both 13 mm high.

Blum lists TANDEM runners for 9, 12, 15, 18 and 21 in drawers, each with a minimum inside cabinet depth. The 21 in TANDEM drawer needs 557 mm (21-15/16 in), so the default 22 1/2 in cabinet takes it on an overlay front.

An inset front moves the runner back by the sub-front plus the drawer front, minus 11.5 mm. With a 1/2 in box front and a 3/4 in inset front, the 21 in runner needs 22.6 in of depth, and the same cabinet drops to the 18 in drawer. The calculator handles MOVENTO with overlay fronts only.

Drawer Box Calculator Cut List by Corner Joint

The joint decides which parts run full length. With butt joints and the front and back set between the sides, the sides equal the box length and the front and back are the box width minus two side thicknesses.

$$L_{fb}=W_{box}-2t+2r$$

The rabbet depth r only counts on a rabbeted box, and each side gets a rabbet at both ends. With the sides inside instead, the front and back run full width and the sides lose two front thicknesses, while dovetails and box joints leave every part at full size.

That choice also decides where a thickness mistake lands on a Blum box. If Baltic birch sold as 1/2 in actually measures 12 mm, a dovetailed box cut from the 1/2 in figure ends up about 1/16 in too wide inside, because the front and back are cut to the outside width. A butt-jointed box with the front between the sides keeps the right inside width, since that front is cut to the inside size.

A grooved bottom reaches into the groove on all four parts, less a little play so it drops in during glue-up.

$$B_w=W_{box}-2t+2g-p$$

For the default box that is 15 15/16 + 1/2 - 1/16 = 16 3/8 in wide, and the same sum on the 21 in inside length gives 21 7/16 in. Ten of those bottoms come out of one 4 x 8 sheet laid two across and five along.

Openings can run 3 to 60 in wide, 1-1/2 to 36 in high and 6 to 36 in deep. A groove or rabbet has to be shallower than the stock it is cut in, and if the gaps and stock leave no room for a box the results stop and ask you to check the opening.

What One Drawer Holds

Storage is measured inside the walls and above the bottom. The default box has 15 15/16 x 21 in inside and 4 1/4 in of usable height once the 1/2 in groove offset and 1/4 in bottom come off, which is about 1,422 cu in or 23 liters.

Side stock is the total run of sides, fronts and backs at box height for all drawers. Four default boxes need about 25.3 ft of 5 in wide stock, before kerf and waste, so plan on more when you buy.

Once the boxes are hung, the fronts come next. The Drawer Pull Positioning Calculator takes the finished front size and marks the knob or pull holes.

What Builders Ask About Drawer Boxes

How much smaller should a drawer box be than the opening?

For side-mount slides like the Accuride 3832EC, build the box 1-1/16 in narrower and at least 1/2 in shorter than the opening. An 18 x 6 in opening then takes a 16 15/16 in box up to 5 1/2 in tall.

Blum undermount boxes follow a different rule. Blum's own table deducts 5/8 in from the opening width for 1/2 in sides and 13/32 in for 5/8 in sides, and the height comes down by 25/32 in for TANDEM.

Do undermount slides need any side clearance?

Yes, even though the runners hide under the box. Blum fixes the inside width at the opening minus 42 mm, which leaves roughly 21 mm from each side of the opening to the inside face of the drawer side.

With 5/8 in sides that works out to about 3/16 in of air on each side. A box built to the full opening width, as some guides suggest, is too wide for the runners, and Blum says the 42 mm rule is what lets them align and run.

How long should the drawer slides be?

Use the longest slide whose real length fits the inside depth, then build the box to the slide's nominal length. For side-mounts that is usually a 22 in slide in a standard base cabinet.

For Blum, check the minimum inside depth rather than the drawer length. The 21 in TANDEM drawer needs 21-15/16 in inside, and an inset front adds the runner setback on top of that.

Where do I measure the opening on a face frame cabinet?

Measure between the face frame stiles for width and between the rails for height. That is the opening Blum means, as a Popular Woodworking guide to TANDEM drawer parts shows.

Behind the frame, the cabinet sides often sit farther out than the stiles. Accuride offers face frame brackets for the 3832EC, and Blum's 563H runners use a rear mounting bracket or blocking in face frame cabinets.