For two equal overlay cabinet doors covering one opening, add the left and right outside overlays to the opening width, subtract the center gap once, and divide by two. Calculate each door’s height separately by adding the top and bottom overlays to the opening height.
The reference chart below uses a 1/2 in overlay at the left, right, top, and bottom of the opening, plus a 1/8 in gap between the doors. These are example inputs—not universal hinge requirements or installation clearances.
Define the Opening, Overlays, and Center Gap
Use the measured cabinet opening, not the cabinet’s nominal size or overall outside dimensions. For a face-frame cabinet, measure between the inside edges of the face frame. Eagle Woodworking’s cabinet door measuring instructions use this opening-based approach and distinguish overlay doors from doors fitted inside the opening.
For this reference:
- Opening width is the width of one opening covered by both doors.
- Opening height is the height of that same opening.
- Outside overlay is the distance each door extends beyond the opening at its outer left or right edge.
- Top overlay and bottom overlay are the distances each door extends above and below the opening.
- Center gap, also called the center reveal, is the space between the two closed doors’ meeting edges.
The chart assumes one uninterrupted opening without a center stile, equal door widths, and equal outside overlays. If a center stile divides the cabinet into two openings, measure and size the doors for that arrangement rather than treating the combined width as one clear opening.
Paired Overlay Cabinet Door Formula
Use the same unit for every input: either inches throughout or millimeters throughout.
For equal doors with matching left and right outside overlays:
[
D_w=\frac{W+2O-G}{2}
]
For each door’s height:
[
D_h=H+O_t+O_b
]
Where:
- (D_w) = finished width of each door.
- (D_h) = finished height of each door.
- (W) = opening width.
- (H) = opening height.
- (O) = overlay at each outside vertical edge.
- (G) = center gap between the doors.
- (O_t) = top overlay.
- (O_b) = bottom overlay.
Subtract the center gap before dividing by two. Subtracting the full gap from each door after division would remove twice the intended allowance.
If the left and right outside overlays differ, replace (2O) with (O_L+O_R). Equal-width doors will then meet away from the opening’s centerline.
Eagle Woodworking publishes the same split-door width method for its 1/8 in center-reveal examples. That supports the calculation method; it does not establish 1/8 in as the required gap for every door and hinge combination.
Paired Overlay Door Size Reference Chart
Every row assumes:
- Outside overlay: 0.500 in at both the left and right edges.
- Top overlay: 0.500 in.
- Bottom overlay: 0.500 in.
- Center gap: 0.125 in.
- Two equal-width doors of the same height.
Dimensions below are finished overall door sizes, not rail, stile, or panel cutting dimensions.
| Opening width (in) | Opening height (in) | Outside overlay (in) | Center gap (in) | Width of each door (in) | Door height (in) |
|---|---|---|---|---|---|
| 24 | 30 | 0.500 | 0.125 | 12.438 | 31.000 |
| 30 | 30 | 0.500 | 0.125 | 15.438 | 31.000 |
| 36 | 30 | 0.500 | 0.125 | 18.438 | 31.000 |
| 36 | 36 | 0.500 | 0.125 | 18.438 | 37.000 |
Decimal results are rounded to the nearest 0.001 in, with halfway values rounded up. The exact widths are:
- 12.438 in displayed: 12.4375 in, or 12 7/16 in exactly.
- 15.438 in displayed: 15.4375 in, or 15 7/16 in exactly.
- 18.438 in displayed: 18.4375 in, or 18 7/16 in exactly.
Keep the unrounded result through the calculation. Three-decimal display precision is not a manufacturing tolerance; rounding the door sizes before checking the assembly can slightly change the implied center gap.
Worked Example: A 30 × 30 in Opening
For a 30 in wide × 30 in high opening, use 1/2 in outside overlays, 1/2 in top and bottom overlays, and a 1/8 in center gap.
Each door’s width is:
[
D_w=\frac{30+0.500+0.500-0.125}{2}
=\frac{30.875}{2}
=15.4375\text{ in}
]
Each door’s height is:
[
D_h=30+0.500+0.500=31\text{ in}
]
The calculated finished size is 15 7/16 in wide × 31 in high for each door.
Check the width by putting the pair back together mathematically:
[
2(15.4375)+0.125=31.000\text{ in}
]
That equals the 30 in opening plus 1/2 in of overlay at each outside edge.
For the same geometry in millimeters, the opening is 762 × 762 mm, each overlay is 12.7 mm, and the center gap is 3.175 mm. Each door calculates to 392.1125 × 787.4 mm before rounding. Substituting a 3 mm gap would describe a slightly different layout, not an exact unit conversion.
Check the Layout Before Ordering or Cutting
Confirm the opening dimensions and intended overlays on the actual cabinet. Check that the top and bottom overlays leave the intended gaps to nearby drawer fronts, doors, and trim; they do not have to equal the outside overlays.
Match the selected overlay and clearances to the specific hinge, mounting arrangement, and door construction. Eagle Woodworking likewise advises matching hinge selection to the intended overlay. The formulas determine a rectangular door size from supplied dimensions; they do not determine hinge boring locations, opening clearance, or final installation fit.
For related resources, the Woodworking Calculator directory lists a Cabinet Door Size Calculator described as sizing overlay or inset single and paired doors from a cabinet opening. Use the chart above as a formula-based reference, not as a record of that calculator’s interface defaults or tested outputs.