Cabinet Drawer Box & Slide Clearance Calculator

Start with the space the moving box can actually use

Measure clear width at the slide mounting surfaces, usable opening height, and depth behind the drawer front. A face frame opening may be narrower than the cabinet interior. Blocking, brackets, hinges, plumbing, and cables can reduce usable space. Measure several positions and resolve a tapered or twisted cabinet first. Review the inherited opening rather than assuming door and drawer geometry match. Keep the decorative drawer front separate from the structural box: its overlay does not add width to the moving box.

Calculate side-mount clearance from the selected slide

For a symmetrical side-mount arrangement, outside box width equals clear opening width minus twice the required per-side clearance. A common planning example uses 1/2 inch per side, giving a one inch total deduction, but the actual slide instructions control. With different left and right requirements, subtract them individually. Slide clearance describes the space between cabinet and drawer, not the drawer side thickness. Increasing the stock thickness makes the inside narrower while leaving this outside width unchanged. Measure stock after milling or purchase; nominal 1/2 inch plywood can differ from the thickness used in the drawing.

Worked example: fronts and backs between the sides

Assume a 24 inch clear opening, 1/2 inch clearance on each side, 1/2 inch drawer stock, a chosen 21 inch box length, and a 6 inch box height. Outside box width is 23 inches. For a butt joint with front and back between full-length sides, cut two sides 21 × 6 inches and two front or back pieces 22 × 6 inches. The clear interior measures 22 inches across and 20 inches front to back. These are geometric sizes before any deliberate fitting allowance; the chosen height and length still need to satisfy the slide installation.

Rabbet engagement changes the front and back lengths

Define where the joint is cut before choosing a rabbet preset. If each front or back enters a 1/4 inch recess in the inside face of a side, its length is outside width minus two side thicknesses plus two engagement depths. The example becomes 23 − 1 + 1/2 = 22 1/2 inches. The outside box remains 23 inches wide. A rabbet cut in the end of a different member can reverse this arrangement; do not apply the equation by joint name alone. Dovetail shoulders and machine setups need their own geometry rather than a guessed universal extra length.

Keep drawer bottom size and vertical position separate

For grooves in all four members, bottom width equals clear internal width plus the left and right groove depths, minus the selected fitting allowance. Bottom length uses the internal front-to-back distance and the corresponding groove depths. With the butt-joint example and 1/4 inch grooves, a zero-allowance geometric bottom is 22 1/2 × 20 1/2 inches. Choose an allowance through a scrap fit test. Groove width follows measured bottom thickness. Groove depth is horizontal engagement; groove height is its vertical position. Neither number alone establishes the clearance beneath the bottom that an undermount runner needs.

Use the TANDEM 563H inside-width rule correctly

Blum's TANDEM 563H instructions specify internal drawer width as clear opening width minus 42 millimeters. Outside width adds twice the measured side thickness, limited to 16 millimeters. For a 600 millimeter opening and 15 millimeter sides, inside width is 558 millimeters and outside width is 588. The drawing requires a 13 millimeter recess from the bottom panel's lower surface to the side's lower edge, not its groove center. It also requires 14 millimeters beneath the drawer and at least 6 above; maximum box height is opening height minus 20 millimeters. These are 563H requirements, not a universal MOVENTO preset.

Select length with the mounting drawing beside you

Choose a runner model before finalizing box depth. Nominal length, actual runner length, drawer length, front setback, and minimum cabinet depth can differ. Rear sockets and brackets consume space. Check face frame or frameless mounting and whether an inset front changes setback. A cabinet described as 24 inches deep does not automatically accept a 24 inch drawer. Treat 15, 18, and 21 inch choices as candidates until their drawings fit the measured interior. For example, 563H5330B uses a 533 millimeter box, 548 millimeter runner, and at least 557 millimeters of cabinet depth. Retain clearance for rear hardware and obstructions throughout travel.

Choose height from the moving assembly, not the front alone

A drawer front can cover a larger opening than its box occupies. Determine the available height from the runner position, bottom clearance, upper obstruction, and the selected hardware. Check brackets, lock devices, and rear hooks against the bottom groove and joint locations. An unnecessarily tall box can hit a rail or a door hinge even when its face closes neatly. For a generic custom installation, record the box height as a deliberate input rather than presenting a guessed recommendation. For a supported manufacturer model, use its drawing and the measured opening to establish the allowed envelope.

Keep precision through the calculation

Use one unit throughout each calculation. One inch equals 25.4 millimeters exactly, so 1/2 inch is 12.7 millimeters rather than 13. A stock label and its measured metric thickness are not interchangeable. Preserve decimal values internally and round fractions only for reading or marking. For example, 588 millimeters is approximately 23.1496 inches; a nearest-sixteenth display becomes 23 1/8 inches and loses 0.625 millimeter. Decide which dimension controls the setup, then work from that value instead of converting the rounded display back into the other unit.

Check the parts against this assembly table

This table describes the 23 × 21 × 6 inch example with fronts and backs between 1/2 inch sides. It records quantities and geometric lengths; fitting allowances and hardware details remain project decisions. Test the first box before duplicating it.

Dry fit, square, and install one drawer first

Mark cabinet number, drawer number, role, and reference face before machining. Match opposing sides and front or back pieces against the same stop. Dry assemble around the bottom, compare diagonals, and inspect whether the groove holds the panel without forcing the sides apart. Clamp without twisting the box. Mount both slides at matching height and depth, following their fastening pattern. Test full travel and engagement before attaching the decorative front. Use the hardware's adjustments to align the front within their stated range; do not rely on adjustments to correct a fundamentally oversized box.

Record the installation conditions with each batch row

Keep the slide model, side thickness, clearance, joint arrangement, bottom engagement, and vertical recess beside the cut sizes. Similar-looking drawers may have different runner lengths or interior obstructions. Label left and right parts consistently even when interchangeable. Review inherited opening dimensions before saving another row. Shared project state reduces repeated typing; it does not replace measurements. Keep workshop notes with the batch so a replacement part can be reconstructed later.

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