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Window and Door Trim Calculator: Casing Pieces and Cut List

Casing 4 picture-frame windows (36 × 48 in) and 3 doors (32 × 80 in, cased on both sides) in 2-1/4 in casing with a 3/16 in reveal takes 26 pieces of 8 ft casing with 10% waste (an estimate), 163.38 linear ft before waste. Each door head is 36.88 in and each door leg 82.44 in, measured to the long point of the miter.

Figures based on the sources listed belowUpdated How we calculate

Waste (estimate)

Windows of the size below. For a second size, run the calculator again and add the results.

The opening from jamb to jamb, in inches (the finished opening the casing goes around, not the rough opening).

Jamb to jamb, in inches, from the sill (or stool) up to the head jamb.
Picture frame trims a window like a door with a bottom piece. Stool and apron has a shelf-like stool at the sill with the apron under it; the side casings stand on the stool.

Doors of the size below. For a second size, run the calculator again and add the results.
Common interior doors are 28, 30, 32 and 36 in wide by 80 in (6 ft 8 in) tall. The casing goes around the jamb opening, which is the door width plus the jamb; the door size is the usual stand-in.

Jamb to jamb, in inches. 80 in (6 ft 8 in) is the common height; taller doors exist.
An interior door is cased on both sides of the wall. An exterior door is usually cased on the inside only.
The face width of the casing. 2-1/4 in is the widely stocked width; 2-1/2 to 3-1/2 in is typical for colonial and craftsman styles.

The strip of jamb left showing between the jamb edge and the casing. 3/16 in (0.1875) is typical; 1/4 in is also common. Mark it with a reveal gauge or a combination square.
The length you will buy. Casing for an 80 in door is often sold as 7 ft (84 in) pieces; 14 ft pieces cut two door legs.

Buy 26 pieces.

Buy 26 pieces

163.38 linear ft + 10% waste = 179.71 linear ft

  • Total casing: 163.4 ft
  • Casing pieces (8 ft): 26 pieces, 23 before waste
  • Cuts needed (inches, long point): 4 × 40.88 in window head; 8 × 52.88 in window leg; 4 × 40.88 in window bottom; 6 × 36.88 in door head; 12 × 82.44 in door leg
  • Cut list (first-fit, inches): 12 × 82.44 in; 8 × 52.88 in + 40.88 in; 3 × 36.88 in + 36.88 in (before waste)
  • Window head casing, each: 40.88 in
  • Door head casing, each: 36.88 in
  • Door leg casing, each: 82.44 in
How this number is calculated

163.38 linear ft + 10% waste = 179.71 linear ft ÷ 6.91 linear ft per piece = 26 pieces

Shopping list

  • Primed door and window casing
  • Window stool (primed pine)
  • Miter saw
  • 18-gauge brad nailer
  • Combination square (to mark the reveal)
  • Wood glue for miters
  • Paintable caulk

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Casing cut lengths by casing width

A 32 × 80 in door and a 36 × 48 in window, 3/16 in reveal, 3/4 in stool horns; all lengths to the long point of the miter. Worked with the same formulas as the calculator.
Casing widthDoor headDoor legWindow headWindow leg (picture frame)Window leg (on stool)Stool
2.25 in36.88 in82.44 in40.88 in52.88 in50.44 in42.38 in
2.5 in37.38 in82.69 in41.38 in53.38 in50.69 in42.88 in
3.25 in38.88 in83.44 in42.88 in54.88 in51.44 in44.38 in
3.5 in39.38 in83.69 in43.38 in55.38 in51.69 in44.88 in

Pieces to buy for doors, by stock length

32 × 80 in doors cased on both sides in 2-1/4 in casing, 3/16 in reveal, 10% waste (an estimate), worked by this calculator with a first-fit cut list.
Doors7 ft pieces8 ft pieces14 ft pieces16 ft pieces
1 door6644
2 doors111166
3 doors171799
5 doors28281514
8 doors44442222

Methodology & assumptions

Enter the size of each opening, jamb to jamb, in inches: that is the finished opening the casing goes around. With the reveal r (the strip of jamb left showing, 3/16 in by default) and the casing width c, a mitered head is cut to opening width + 2r + 2c, measured to the long point of the miter. A door leg is opening height + r + c, because a door has no bottom casing and the leg runs from the floor to the long point at the head. A picture-frame window has a bottom piece the length of the head, and its legs run the full height: opening height + 2r + 2c. A stool-and-apron window has no bottom casing; the legs stand on the stool, so they are opening height + r + c, the apron is cut to the length of the head casing, and the stool is the head length plus a horn at each end (3/4 in by default). Interior doors are cased on both sides of the wall; windows on the inside only. All casing pieces, including the aprons, are packed onto stock pieces of the length you pick, longest first, each on the first piece with room (first-fit decreasing); stools are packed separately onto their own stock. Miter angles and saw kerf are not modeled: the waste percentage you choose (10% standard, 15% for a first job or stained trim; both estimates, not standards) is added to the packed piece count and rounded up. If any piece is longer than the stock you picked, the calculator says so instead of giving a count. Nails, glue and caulk are not counted, because no published rate was found for them that applies to every job.

  • Fine Homebuilding, "Case a Door with Mitered Trim": a reveal of about 3/16 in between the jamb edge and the casing, scribed with a combination square or reveal gauge; head casing installed first, then the legs
  • The Home Depot, door casing installation guide (PDF): the head casing is the inside measurement plus twice the reveal (a 36 in opening with a 3/16 in reveal gives 36-3/8 in, short point to short point); this calculator uses the long-point method, which adds the casing width at each end
  • Journal of Light Construction (JLC), "Fitting a Window Stool": stool length from the jamb width plus twice the casing width, the reveals and the horns; horns of 3/4 to 1 in past the casing. Fine Homebuilding and This Old House describe horns of about the casing thickness to 1 in. A style choice, so the default of 3/4 in is a typical value
  • Door casing sets: casing for an 80 in door is commonly sold as 7 ft (84 in) lengths and sets, for example the 2-1/4 in x 7 ft finger-jointed sets listed by large home centers
  • Common interior door sizes of 24, 28, 30, 32 and 36 in wide by 80 in tall, and casing widths of 2-1/4 in (the widely stocked residential width) to 3-1/2 in (colonial and craftsman styles): manufacturer and retailer size charts. These are typical, so check your own openings and your supplier
  • Waste of 10 to 15% for mitered casing: a common rule of thumb in trim calculators, not a standard (an estimate)

How to figure window and door casing and a cut list

  1. Measure each opening. Measure the jamb-to-jamb width and height of a window or door in inches, and count how many of each size. For a second size, run the calculator again and add the pieces.
  2. Choose the casing and reveal. Pick the casing width, and keep or change the 3/16 in reveal. Choose picture-frame or stool-and-apron for the windows, and one or both sides for the doors.
  3. Pick the stock length and waste. Choose 7, 8, 14 or 16 ft casing (7 ft suits door legs) and 10 or 15% waste. For stools, pick the stool length and the horn.
  4. Read the pieces and cuts. Buy the number of pieces shown, and use the cuts needed and the cut list to see which lengths come from which piece.
  5. Cut, test and trim. Cut a head to the long point and fit it on the jambs with the reveal marked, then cut the legs to fit. Test the miters on scrap before cutting good stock.

Worked examples

ProjectResult
4 windows 36 × 48 in and 3 doors 32 × 80 in cased both sides, 2-1/4 in casing, 8 ft pieces, 10% waste26 pieces (12 × 82.44 in; 8 × 52.88 in + 40.88 in; 3 × 36.88 in + 36.88 in before waste)
6 windows 36 × 60 in, stool and apron, 3-1/2 in casing, 8 ft pieces, 10% waste20 pieces (12 × 63.69 in; 6 × 43.38 in + 43.38 in before waste) plus 3 stool pieces of 8 ft before waste
2 exterior doors 36 × 80 in cased on one side, 3-1/2 in casing, 7 ft pieces, 15% waste7 pieces (4 × 83.69 in; 2 × 43.38 in before waste)
8 doors 30 × 80 in cased both sides, 2-1/2 in casing, 14 ft pieces, 10% waste22 pieces (16 × 82.69 in + 82.69 in; 4 × 35.38 in + 35.38 in + 35.38 in + 35.38 in before waste)
One custom door 34-1/2 × 84 in cased both sides, 2-1/4 in casing, 8 ft pieces, 10% waste6 pieces (4 × 86.44 in; 1 × 39.38 in + 39.38 in before waste)

Frequently asked questions

How much casing do I need for a door?
A door has a head and two legs and no bottom piece. With 2-1/4 in casing and a 3/16 in reveal, a 32 × 80 in door takes one head of 36.88 in and two legs of 82.44 in, which is about 16.8 linear ft per side of the wall before waste. An interior door is cased on both sides, so double it. The calculator packs the pieces onto stock lengths, so the offcut of one cut can finish another.
How do I figure the length of the head casing?
Long point to long point, the head is the opening width + 2 × the reveal + 2 × the casing width: a 36 in door opening with a 3/16 in reveal and 2-1/4 in casing is 40.88 in. Some guides give the short-point length instead (36 + 2 × 3/16 = 36-3/8 in); the long point is what you mark on the stock when the miter cuts away the ends.
How long are the side casings (legs)?
Long point to square end, a door leg is the opening height + reveal + casing width, because the leg runs from the floor to the head. An 80 in door with 2-1/4 in casing gives 82.44 in. That is why door casing is often sold in 7 ft (84 in) lengths: it just fits one leg, with about 1-1/2 in to spare.
What is the reveal and what should it be?
The reveal is the strip of jamb left showing between the inside edge of the jamb and the casing. About 3/16 in is the most common, and 1/4 in is also used; what matters is that it is the same on every side of the opening. It is a look, not a code figure, so the calculator lets you change it. Mark it with a reveal gauge or a combination square, and every length on this page follows from it.
What is the difference between picture-frame and stool-and-apron windows?
A picture-frame window is cased on all four sides like a door with a bottom piece, so it takes a head, two legs that run the full height, and a bottom the length of the head. A stool-and-apron window has a shelf-like stool at the sill with an apron under it: the legs stand on the stool, so they are shorter by the reveal and casing width at the bottom, and the apron is cut to the length of the head. Six 36 × 60 in stool-and-apron windows in 3.5 in casing take 20 pieces of 8 ft casing and 4 stools.
How far should the stool horns stick out?
The horns are the ends of the stool that run past the side casings. About 3/4 in beyond the casing is typical; trim carpenters use anything from about 1/2 in to 1 in, and it is a matter of taste. The stool is notched around the jambs, so cut it a little long and scribe it to the wall. The calculator uses the horn you enter in the stool length, which is the head length + 2 × the horn.
What stock lengths are casing and stools sold in?
Casing is commonly sold in 7 ft (84 in) lengths and sets for doors, and in 8, 14 and 16 ft lengths. Your supplier decides what is stocked, so check before you plan around one length. Seven-foot pieces suit door legs; 14 and 16 ft pieces cut several shorter head and window pieces from one length. Stools vary by supplier and the 6, 8 and 12 ft choices here are typical lengths, not a standard.
How are the pieces packed?
All the casing pieces (and aprons) are sorted from longest to shortest and each is put on the first stock piece with room left, so an offcut can finish another cut. Eight 30 × 80 in doors cased on both sides in 2.5 in casing on 14 ft pieces take 22 pieces with 10% waste (16 × 82.69 in + 82.69 in; 4 × 35.38 in + 35.38 in + 35.38 in + 35.38 in before waste). Miter angles and kerf are not modeled, which is what the waste percentage is for.
Do I count both sides of an interior door?
Yes. Interior doors are cased on both faces of the wall, so each door takes two sets of casing. The calculator defaults to both sides; switch to one side for an exterior door cased on the inside only, or for a closet opening trimmed on one face.
How much waste should I allow?
Ten percent covers mitered casing on a straightforward job, and 15% is a safer allowance for a first job, stained trim that must be matched, or walls that are out of square. These are rules of thumb, not standards. Remember that casing is packed whole pieces, so the real spare is often larger than the percentage.
Does it count nails, glue or caulk?
No. Brad nails, miter glue and paintable caulk are the usual finish and are cheap to keep on hand, but no published coverage rate applies to every job, so the calculator leaves the count to you instead of guessing. The shopping links list the tools and supplies that usually go with the job.

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