How to use it
Measure the opening
Measure the opening of the case as built, not the drawing: width between the sides or face-frame stiles, height between top and bottom. Check the diagonals; if they differ, the opening is out of square and no single door size fits it exactly.
Choose overlay or inset
Overlay doors sit in front of the case and cover part of its edges; inset doors sit inside the opening, flush with the front.
Enter the edges
For overlay, enter how far the door covers the case at each edge — the figure your hinge and mounting plate give. For inset, enter the reveal you want at each edge: the gap between door and opening.
For a pair, enter the gap
Two doors share the width, less one gap between them. The gap is counted once, never at each door.
The geometry
Overlay
covered width = opening width + left overlay + right overlay
door height = opening height + top overlay + bottom overlay
one door: width = covered width
a pair: each width = (covered width − gap) ÷ 2
Inset
covered width = opening width − left reveal − right reveal
door height = opening height − top reveal − bottom reveal
one door: width = covered width
a pair: each width = (covered width − gap) ÷ 2
Worked example: a 30 × 30 in opening with a pair of overlay doors, 1/2 in overlay on every edge and a 1/8 in gap. The covered width is 30 + 1/2 + 1/2 = 31 in, so each door is (31 − 1/8) ÷ 2 = 15-7/16 in wide and 30 + 1/2 + 1/2 = 31 in tall. Check: 15-7/16 + 1/8 + 15-7/16 = 31.
Overlays come from the hinge
How far a concealed hinge lets a door cover the case is a property of the hinge, its mounting plate and where the cup is bored, so no figure here is a default. Blum's kit for one of its frameless hinges, for example, offers overlays from 14 to 18 mm, each tied to a cup centrepoint from 20.5 to 24.5 mm from the door's edge, and positions the mounting plate from the bottom overlay. A different hinge, plate or cabinet style gives different figures. Enter yours from your own hinge's instructions; asymmetric openings — a door beside a shared partition, for instance — may need a different overlay on each side, which is why each edge is a separate field.
What the result does not include
- Hinge fit. Whether your hinge can give the overlay you entered, on your door's thickness and weight, is in the hinge maker's data.
- An out-of-square opening. The calculator assumes a rectangle; check the diagonals before relying on one size.
- Finish and edge banding, which add thickness to a door's edges.
- Wood movement. A solid-wood door or a frame-and-panel door's panel changes width with moisture, as the Wood Handbook explains; see the wood movement calculator.
- Door construction. Rail, stile and panel sizes for a frame-and-panel door are not calculated.
Published plans that need doors use them in their own way: BenchRoot's cabinet plans use sliding doors, which this calculator does not size, so no hinge figures are needed. Measuring real plywood is covered in the plywood thickness chart, the order in which doors are made in learning furniture making, and drawer boxes and fronts in the drawer size calculator.
Safety— Measure, then cut a test door
The figures are planning dimensions. Measure the actual opening, check the hinge maker's overlay, and fit one door before cutting the rest. Cabinets that hold heavy doors on a wall need fixings chosen from their makers' data; see woodworking safety rules for the shop rules.
Before cutting doors
- The opening measured on the case as built, diagonals checked
- Overlay or reveal for each edge from the hinge maker or your plan
- For a pair, one gap between the doors
- Finish or banding thickness allowed for
- One door fitted before the rest are cut
Sources
The arithmetic is plain geometry and is tested against hand-worked examples. The calculator assumes no hinge, overlay, reveal or gap: every one is entered. Blum's figures are cited only as an example of overlay being set by the hinge, not as a default. Results are planning dimensions: the opening must be measured, and the hinge maker's figures checked, before parts are cut.
- 1.
Kit Instructions H002: CLIP top BLUMOTION 110° (soft close) hinge. Blum, Inc., 2025.
Used for: An example of overlay belonging to the hinge: Blum's kit for its CLIP top BLUMOTION 110° hinge, for frameless cabinets and doors 16 to 26 mm thick, sets an overlay of 14 to 18 mm by the hinge cup's centrepoint (20.5 to 24.5 mm from the door edge), and positions the mounting plate from the bottom overlay (Y = X − OL).
- 2.
Chapter 4: Moisture Relations and Physical Properties of Wood. USDA Forest Service, Forest Products Laboratory — Wood Handbook, FPL-GTR-282, 2021.
Used for: Solid wood changing in width across the grain as its moisture content changes, which door-size arithmetic does not include.
About this calculator
Written by BenchRoot Editorial. How BenchRoot sources, checks and corrects its pages is set out in the Editorial Policy. If something here is wrong or unclear, the contact page explains how to tell us.