For a single inset cabinet door, subtract the left and right reveals from the opening width, and subtract the top and bottom reveals from the opening height. With a 1/8 in reveal on every edge, the door is 1/4 in narrower and 1/4 in shorter than the opening. A 12 × 24 in opening therefore gives a calculated door size of 11-3/4 × 23-3/4 in.
The reveal is the visible gap between the closed door edge and the surrounding opening. The 1/8 in reveal used below is a selected design input, not a universal installation requirement.
Inset Cabinet Door Size Reference Table
Each row represents one rectangular inset door within one opening. Opening dimensions are the clear dimensions where the door will sit—not the cabinet’s outside dimensions or the dimensions of an existing door.
All dimensions are in inches. The reveal applies separately to each of the four edges.
| Opening width (in) | Opening height (in) | Reveal per edge (in) | Door width (in) | Door height (in) |
|---|---|---|---|---|
| 12 | 24 | 0.125 | 11.750 | 23.750 |
| 15 | 30 | 0.125 | 14.750 | 29.750 |
| 18 | 30 | 0.125 | 17.750 | 29.750 |
| 24 | 36 | 0.125 | 23.750 | 35.750 |
These are formula-derived dimensions, not standard cabinet opening sizes or hardware-approved door sizes. Results are shown to three decimal places; every value in this table is exact for the stated inputs. The displayed precision does not specify a fabrication tolerance.
How to Calculate Inset Door Dimensions
Use the following formulas when the reveals differ by edge:
[
W_d = W_o – r_L – r_R
]
[
H_d = H_o – r_T – r_B
]
Where:
- (W_d) = finished door width.
- (H_d) = finished door height.
- (W_o) = clear opening width.
- (H_o) = clear opening height.
- (r_L), (r_R), (r_T), and (r_B) = left, right, top, and bottom reveals.
Use the same unit for every dimension. For an equal reveal (r) on all four edges:
[
W_d = W_o – 2r
]
[
H_d = H_o – 2r
]
The opening width must exceed the combined left and right reveals, and the opening height must exceed the combined top and bottom reveals. A zero or negative calculated dimension is not a usable door size.
Example: A 12 × 24 in Opening
With a 1/8 in reveal at each edge:
- Door width = 12 − 1/8 − 1/8 = 11-3/4 in.
- Door height = 24 − 1/8 − 1/8 = 23-3/4 in.
The total reduction is 1/4 in in each direction—not 1/8 in. Check the result by adding both opposing reveals back to the door dimension: 11-3/4 + 1/8 + 1/8 = 12 in.
Using Millimeters
The formulas work unchanged in millimeters. The exact equivalents for the same example are:
- Opening: 304.8 × 609.6 mm.
- Reveal per edge: 3.175 mm.
- Calculated door: 298.45 × 603.25 mm.
A 3 mm reveal is a different input from a 1/8 in reveal. Keep intermediate values unrounded, then choose a final measurement increment appropriate to the project. Recheck the resulting gaps after rounding.
Measure the Opening and Select the Reveal
Measure width at the top, middle, and bottom, and height at the left, center, and right. Compare the diagonals to check whether the opening is square. If measurements vary, do not assume that one width and height will produce an even reveal around a rectangular door; resolve the opening geometry and fitting approach first.
Use finished opening dimensions and finished overall door dimensions as the calculation basis. If measuring before finishing, account for any coating or edge treatment that changes those dimensions. These formulas do not calculate rail, stile, or panel sizes, and they do not include extra stock for trimming during fitting.
Select the reveal alongside the hinge specification. A visually suitable gap is not automatically sufficient for the door to swing clear. Consult the planning information for the exact hinge, mounting plate, door thickness, and drilling arrangement. For example, the Blum 2022/2023 technical manual, page 95, gives a minimum-gap table specifically for its blind-corner inset application, with stated front-radius and mounting conditions; those values are not general inset-door requirements.
Related Cabinet Door Calculator
The Woodworking Calculator directory lists a Cabinet Door Size Calculator for overlay or inset single and paired doors. The reference table above addresses only a single inset door; it does not include the center gap required between paired doors.
Use the calculated dimensions as planning targets, then confirm the actual opening, finished dimensions, and hardware clearances before cutting or ordering the door.