The width is not what costs you — the height is
Put a 12 by 14 ft opening in a 16 ft wall framed with girts at 24 inches. Eight girt rows land on that wall; the opening crosses six of them and leaves two running above the head. Six rows times twelve feet is 72 lineal feet of girt that does not get bought.
Against that, two jamb plies each side at 14 ft is 56 feet, and a two-ply header at 13 ft is 26 feet. That is 82 feet in against 72 feet out — ten feet of net framing, on an opening 12 feet wide. The width barely registers. What drives both sides of the ledger is the height: it sets how many rows get cut, and it sets how long the jambs are.
| Opening | Rows crossed | Girt out | Jamb + header in | Net |
|---|---|---|---|---|
| 3 x 4 ft window | 1 | 3 ft | 22 ft | +19 ft |
| 3 x 7 ft walk door | 3 | 9 ft | 36 ft | +27 ft |
| 10 x 10 ft overhead | 4 | 40 ft | 62 ft | +22 ft |
| 12 x 14 ft slider | 6 | 72 ft | 82 ft | +10 ft |
| 20 x 14 ft slider | 6 | 120 ft | 98 ft | -22 ft |
Every figure above is for a 16 ft wall with 24 inch girts, two jamb plies and a two-ply header with six inch bearing, which is the arrangement the calculator starts on. The pattern is consistent: small openings cost framing feet outright, and only a genuinely wide one gives more back in girt than it takes in jamb and header. The break-even width at 14 ft high on this arrangement is about 14.5 feet, and the calculator prints it for whatever height and spacing you enter.
Feet are the wrong unit anyway
The 12 by 14 opening above is nearly a wash in lineal feet, which makes it sound cheap. Look at what happens to the pieces instead. Before the opening, the two bays it touches held twelve girt pieces at 8 ft each — six rows across two bays. After, those twelve 8 ft pieces are gone and in their place are twelve 2 ft stubs, four 14 ft jamb members and two 13 ft header members. Eighteen pieces where there were twelve, and the twelve that remain are offcut-length stubs that have to be measured, cut, fitted and fastened at both ends like any other piece.
In sticks of 16 ft the before figure is six and the after figure is eight. Two extra sticks does not sound like much either, until you notice that the stubs came out of stock that could have been girt somewhere else, and the four 14 ft jambs each strand two feet. The honest summary of a door opening in a post-frame wall is that it does not save you material and it costs you a lot of cutting.
Whether a post lands inside it changes everything
The calculator places the post lines by dividing the wall evenly and then checks whether any of them fall between the two edges of the opening. On the default numbers — a 40 ft wall in five 8 ft bays, opening starting 2 ft from the corner and running to 14 ft — the post at 8 ft is inside the opening.
That is not a framing detail, it is a structural one, and this page stops at naming it. Whatever the post was carrying still has to be carried, and the header over a door bent is a different member from a header over an opening that fits inside a bay. Which one you have is a question for the plan or the engineer who sealed it. What the calculator can tell you is the cheap version of the question: slide the opening 2 ft toward the corner so its edges land on the post lines at 0 and 16, and the stubs disappear, the bays it touches stay at two, and the post at 8 ft is still inside it. Slide it the other way and you get different stubs. There is no arrangement of a 12 ft opening on 8 ft bays that avoids a post; that takes a 16 ft opening on the module, or 12 ft bays.
What sits at the edges of this
The opening size itself — how wide a door has to be for what goes through it — is a different question, and the machine shed door width and height calculator works it out from the machines you measure. For the door hardware, the pocket and barn door calculator sizes the leaf, the track and the mounting board, and the garage door opening and headroom calculator handles headroom, backroom and sideroom for a sectional door. The bay grid this page checks against comes from the post-frame bay layout calculator, and the panel and trim around the finished opening from the wall panel and wainscot take-off. Header sizing is not done anywhere on this site by design, but the header and beam load calculator shows what the load question involves.
Questions people ask
Does a wide opening really save framing material?
In lineal feet, past a certain width, yes — and the calculator prints the width where it flips for your numbers. On a 16 ft wall with 24 inch girts, a two-ply header and two jamb plies, the crossover at 14 ft opening height is about 14.5 ft wide. Below that the jamb and header outweigh the girt you delete; above it the girt wins. But feet are a misleading unit here. The piece count goes up at every width, the offcut waste goes up, and the header over a wide opening is a bigger member than the one over a narrow one, which the footage comparison ignores entirely because this page counts plies, not sizes.
What happens to the girt rows above the door?
They keep running. A row above the head of the opening spans the same bay it always did, except that where it crosses the opening it has nothing under it but the header, and at each end of the opening it lands on the jamb rather than on a post. That is why the jamb runs full height in this take-off rather than stopping at the header: it is the thing the girts above the opening bear on where the post used to be. How that connection is made, and whether the jamb is adequate for it, is a plan question. The calculator counts the rows above the head separately from the rows it crosses so you can see how many of them are involved.
Why are the girt stubs beside the opening counted as new pieces if the girt was already there?
Because the piece that was there is not the piece you end up with. A full-bay girt runs post to post at, say, 8 ft. With an opening 2 ft in from the post, that 8 ft piece becomes a 2 ft stub and the rest is opening. You do not cut the 8 ft piece and use the offcut somewhere else in any practical way, because the offcut is 6 ft of a nailed-in-place member. So the cut list changes from twelve 8 ft pieces to twelve 2 ft pieces, and both the number of cuts and the number of fastened ends stay the same while the material in the wall drops. The footage falls and the labour does not.
Can I use this for a window instead of a door?
Yes — set the sill height above zero and the calculator adds a sill member below the opening as well as the header above it, using the same ply count you gave for the header, and it counts the girt rows below the sill separately as untouched. A window is the case where the arithmetic is most lopsided: a 3 by 4 ft window on a 16 ft wall crosses one girt row, so it removes three feet of girt and adds a jamb, a header and a sill totalling around twenty-two feet. Small openings are almost pure addition. Whether the sill member is the right detail for your wall and your cladding is a plan question, not one this page answers.
What is the header bearing figure doing?
It lengthens the header at each end so it lands on something rather than stopping dead at the edge of the opening. Six inches each end on a 12 ft opening makes a 13 ft header, which is why the header footage is more than the opening width. The figure comes from the plan or the engineer, not from here, and the calculator does nothing with it beyond adding it to the length — it does not check whether the bearing is enough, what it bears on, or whether the jamb under it can take the reaction. Those are the questions the bearing figure exists to answer, and they are answered by whoever designed the building.