Choose the assembly that will actually be built
A three-piece door has two legs and a head. A four-sided window closes the bottom with casing. A stool-and-apron window uses a projecting stool and a separate lower member, with dimensions and profiles distinct from the side casing.
Choose the joint arrangement before reading cut lengths. A mitered head meets the legs at their angled ends; a square head-over-legs arrangement has different piece relationships. Changing the joint is more than changing a saw angle on the same length list.
Worked layout
Three-piece mitered door casing
Example measurements
- Inside reference
- 36 × 80 in
- Actual casing face
- 2½ in
- Faces / quantity
- One face, one opening
Layout result
- Visible face
- 2.5 in
- Pieces
- 3
- Exact length
- 17 ft 2 in
Keep jamb-inside and trim-inside measurements separate
Jamb-inside mode starts with the clear jamb opening and adds the reveal you enter. Trim-inside mode starts at the final inside casing line, with reveal already included in that measured reference. Do not add reveal a second time.
Measure width at the head and lower opening and both side heights. Label the actual inside and outside edges of a profile sample. Check the outside footprint beside hinges, walls, tile, and blinds; a wider casing can conflict even when the inside opening is unchanged.
Read role, end direction, long point, and short point
The long point is the outside tip of the mitered casing piece and the short point is the inside tip. A door leg’s lower stop differs from a closed window side’s lower miter. Follow the head, left, right, and bottom labels in the drawing and piece list.
Stool depth, thickness, overhang, and apron face and inset define separate manufacturing blanks. The stool’s jamb notches and final projection still need fitting on site. Do not treat an unnotched rectangular blank as the finished stool profile.
Assign a profile to each physical assembly
Use different assembly records for doors or windows with different profiles or measurements. Select both faces only when the real conditions on both sides match. A quantity multiplier repeats the measured assembly; it cannot verify another opening.
Keep casing, stool, and apron stock in their actual profile groups. Enter available lengths, kerf, end trim, and spares, then inspect the longest piece in each group. Unknown or different profiles must not be mixed simply because their lengths fit the same board.
Test the actual corner before repeated cuts
Dry-fit a sample using the intended profile and reveal. Check real corner angles and the wall plane before treating opposite sides as interchangeable. An overlong member needs suitable stock or an explicitly supported joint; the purchase estimate must not silently split it.
Arches, compound miters, layered pediments, rosettes, plinth blocks, and jamb fabrication require additional measured details. This trim plan does not size structural headers, rough openings, flashing, or egress.
Door and Window Trim Calculator questions
Do I add reveal to a trim-inside measurement?
No. That reference already locates the final inside casing line. Enter reveal separately only when starting from jamb-inside measurements.
Can I plan stool and apron trim?
Yes. Supply its separate dimensions and material profiles. The stool’s jamb notches and final fit remain on-site work.
Can different casing profiles share one stock count?
Only when their material compatibility is explicitly established. Different or unknown profiles must remain separate purchase groups.