Short answer
One side of a 32 x 80 in door with 2-1/4 in mitered casing takes about 17 linear feet: two legs of about 82-1/2 in and a head of about 37 in. Trim both sides and it is about 34 feet. That fits three 7 ft lengths per side, but casing wider than about 2-3/4 in makes mitered legs too long for 7 ft stock.
You need
How the calculator works
- Legs. With a mitered head, each leg runs from the floor to the long point of the miter: door height + 3/16 in reveal + casing width. With a butted head, the leg stops under the head: door height + reveal.
- Head. Door width + two reveals gives the short points (Home Depot guide); add two casing widths for the long points. A butted head also overhangs each leg slightly; the calculator adds 3/8 in a side, a common carpenter's choice (JLC).
- Allowance. One inch per piece to square factory ends and recut a miter that does not close. Pieces are packed into your stock length, longest first.
- Extra. The optional 10 or 15 percent adds spare pieces for mistakes, warped boards and a matching piece later.
Common door sizes
Finished linear feet, mitered head, 3/16 in reveal, no allowance
| Door | One side, 2-1/4 in casing | Both sides |
|---|---|---|
| 24 x 80 in | 16.1 ft | 32.3 ft |
| 30 x 80 in | 16.6 ft | 33.3 ft |
| 32 x 80 in | 16.8 ft | 33.6 ft |
| 36 x 80 in | 17.1 ft | 34.3 ft |
| 36 x 96 in | 19.8 ft | 39.6 ft |
Interior doors are most often 80 in tall and 24 to 36 in wide (Bob Vila). Trimming many doors at once? A precut trim kit can save the miter cuts, and the install guide covers the rest.
Questions people ask
How do you calculate door casing?
Per side of one door: two legs and one head. With mitered corners, each leg is the door height plus the reveal plus the casing width, measured to the long point. The head is the door width plus two reveals plus two casing widths. Add an inch or so per piece to square the ends and true the miters.
How many linear feet of trim for one door?
About 17 feet per side for a 32 by 80 inch door with 2-1/4 inch casing, or about 34 feet for both sides. Fixr also suggests planning on at least 17 linear feet per door.
Will 7 foot casing work for an 80 inch door?
Usually, with standard 2-1/4 inch casing: each mitered leg is about 82-1/2 inches, inside the 84 inches of a 7 foot piece. With casing much wider than about 2-3/4 inches, mitered legs run past 84 inches, so buy 8 foot stock or use a butted head.
What reveal does the calculator use?
A 3/16 inch reveal, the setback Fine Homebuilding and the Home Depot installation guide both use as typical. Change it on the wall if you like a different look; the difference in length is tiny.
Sources
Last reviewed October 12, 2026. Profiles, sizes and listings change; check the product details before you buy, and follow the maker’s instructions.