Installing Windows and Exterior Doors

What this calculation does not cover

• One length, several different products. A flat sheathing seam takes a straight tape; an inside or outside corner takes a stretch or flexible tape that will turn the angle without tenting; a round penetration or a lapped transition often takes liquid-applied flashing and no tape at all. Those are separate purchases in separate widths sold in fixed roll lengths, and one total silently averages them — buy against it and the corners are the part that comes up short.
• Taping the perimeter of a rough opening is an AIR seal, not a water detail. Water needs a sloped or pan-formed sill and laps that shingle downward, head over jamb over sill, so anything getting past the window is led back out. Tape run continuously around an opening as an air seal can instead hold water against the sheathing, and that failure shows up as rot at the sill years before anyone opens the wall.

What this calculation does not cover

• The perimeter is taken exactly as entered — the calculator never sees the lite's width and height, so it cannot check that the figure is 2 × (width + height). Entering width plus height instead of the full perimeter halves the answer, and nothing on the page flags the error.
• One perimeter run is counted per lite. Glazing systems that carry both an inner and an outer gasket, or a wedge on one face with tape or a heel bead on the other, need two runs per lite, so either the perimeter or the lite count has to be doubled.
• Wedge gasket is meant to be cut slightly long and compressed into the pocket rather than stretched, because stretched material retracts and opens gaps at the corners. The waste allowance covers offcuts and splices, not that deliberate over-length: on 20 lites of 4.5 m the 5% allowance is 4.5 m, and cutting every leg 3% long consumes 2.7 m of it before a single offcut is made.
• The answer is a pooled length, not a buying quantity or a cut list. It does not know the supplied coil or roll length, so it neither rounds up to whole rolls nor accounts for the drop left at each roll end — 94.5 m (310 ft) bought in 30 m (98 ft) coils means four coils, and no single leg can bridge a coil end.
• This counts linear length only; it does not select a gasket profile. It says nothing about whether the wedge size suits the clearance between the glass edge and the frame rebate, or whether the resulting compression, edge cover and pocket depth meet the system's air and water penetration rating — an undersized wedge leaves the glass loose, an oversized one loads the glass edge.

What this calculation does not cover

• The whole estimate is locked to one figure — a 1/4 in (6 mm) bead at 25 linear ft (7.6 m) per 10.1 oz tube — and there is no field for gap width or joint depth, so the answer never moves when the joint does. Widening the bead to 3/8 in (9.5 mm) at the same depth uses about half as much caulk again per unit length, and a gap that is both wider and deeper can take more than double. Size the bead against the actual gap before ordering to this number.
• It measures the opening, not the bead path. The exterior bead runs around the outside of the casing where trim meets siding, which is longer than the opening perimeter by roughly eight times the casing width, and most exterior details also take a second bead on the inner edge where casing meets the frame. The waste allowance on the result, 10% as the page opens, does not stand in for either.
• The formula takes the full perimeter, 2 x (height + width), so it charges caulk along the bottom of every opening. Standard practice on many window and door details is to leave the sill joint and any weep openings deliberately open so water that gets behind the trim can drain out. If you follow that, the real bead is shorter than the figure here.
• Nothing here addresses the sealant itself: substrate compatibility, the movement the joint has to survive, whether a backer rod is needed to set depth and break the third-side bond, primer, or the temperature and surface-moisture limits printed on the cartridge. A correct tube count applied to a joint bonded on three sides still tears through its own middle.
• This is a material take-off, not an air-sealing assessment. It does not identify where the leaks are, and it is not a blower-door result or evidence of compliance with any air-leakage or energy-code requirement — trim caulk is one small part of a wall's air barrier.

What this calculation does not cover

• The stick figure is a length division — the run with waste divided by the stock length and rounded up — and it takes no account of which piece has to come out of which stick. A 2.032 m door leg cut from an 8 ft (2.44 m) stick leaves 406 mm, too short for the 864 mm head, so four identical doors take ten sticks on the bench against the nine that division returns. Openings of different sizes have to be run separately and their stick counts added, because offcuts from one run are not pooled into another.
• No casing width is collected, so the run is the bare opening and nothing else. A mitred picture frame round a window adds about eight times the casing width, since each of the four pieces runs past the opening at both ends: 456 mm for a 57 mm profile and 712 mm for an 89 mm one. A door adds about four times the casing width, roughly 0.75 linear ft on a standard opening with a 2 1/4 in architrave, which is already half of the default 10% allowance before a single mitre offcut is cut.
• Rough opening, finished jamb and door leaf are three different heights and the calculator simply uses whichever you type. The 2.032 m default is an 80 in leaf rather than a rough opening, and it is not the leg length either: a leg is cut from the finished floor to the top of the head casing, which with an 89 mm architrave over that leaf sits past 2.13 m and will not come out of a 2.1 m stick at all, even though the total-length arithmetic accepts that stock length without complaint.
• The window option assumes a four-sided picture frame. A window finished with a stool and apron is cased on three sides instead, so the four-sided figure overstates it by one opening width per window — 0.9 m on a 1.2 m by 0.9 m opening — while the stool itself, which runs past the legs by a horn at each end, and the apron beneath it are different sections this page does not produce.
• Plinth blocks and corner rosettes change the geometry the figure assumes: a plinth block takes its own height, commonly 130 to 150 mm, off the foot of each leg, and rosettes remove the mitres so the head is cut square between them rather than long-point to long-point. Extension jambs or a jamb rip, needed wherever the wall finish stands proud of the jamb face, are a separate material in a separate width and are outside this total. The height and width fields stop at 3 m, so a 12 ft (3.66 m) patio slider or a wide bifold opening has to be split across runs.