Buttonhole Spacing Calculator
Five buttonholes have four gaps. Dividing by the count instead leaves the last hole four inches short.
Where each one goes
Divide by the gaps, not by the buttonholes
Five buttonholes between a fixed top and a fixed bottom have four gaps between them. So the spacing is the span divided by four, not by five. It is the fencepost problem — count the posts and you get the fences wrong — and it is the single most common error in laying out a placket.
Dividing by the count instead leaves the last hole short of where it should be. Over a 20 inch span:
| Buttonholes | Correct spacing | Dividing by the count | Last hole lands short by |
|---|---|---|---|
| 4 | 6.667″ | 5.000″ | 5.00″ |
| 5 | 5.000″ | 4.000″ | 4.00″ |
| 6 | 4.000″ | 3.333″ | 3.33″ |
| 7 | 3.333″ | 2.857″ | 2.86″ |
| 8 | 2.857″ | 2.500″ | 2.50″ |
And fewer buttonholes make it worse, which nobody expects. With eight holes the mistake costs two and a half inches; with four it costs five. The relative difference between n and n − 1 grows as n shrinks, so the sparse plackets where a misplaced hole is most visible are also where the error is largest.
Placing the first and last
- Put one at the fullest point. On a shirt or blouse that is the bust; on a coat it is usually the waist. Gaping happens where the strain is, and a buttonhole exactly there is what prevents it — space the others around it rather than the reverse.
- The top one sits half a button width below the neckline seam, so the button itself does not ride over the edge.
- The bottom one need not be at the hem. Ending three or four inches up is normal and stops the front flaring open when you sit down.
- Horizontal holes take strain better and are used on plackets and waistbands; vertical ones sit on a narrow band where there is no room to go across, and they let the button slide under load.
- Mark from one end only. Measuring each gap from the last mark accumulates every small error down the placket — measure every position from the top.
Buttonhole length is not the button diameter
A hole cut to the button's diameter grips, because the button has to turn edgewise to pass through and its thickness then matters as much as its width. The working rule is diameter plus thickness plus about an eighth of an inch of ease. A thick shank button or a domed one needs noticeably more than a flat disc of the same width, which is why the thickness is a separate box here rather than an assumption.
How to use
- Fix where the first and last buttonholes go, then say how many.
- Put one at the bust or the waist — the point that gapes.
- Mark every position from the top, never gap by gap.
- Cut each hole to the button diameter plus its thickness plus ease.
Frequently asked questions
How do I space buttonholes evenly?
Divide the span between the first and last by the number of GAPS, which is one fewer than the number of buttonholes. Five holes between a fixed top and bottom have four gaps between them, so a 20 inch span gives 5 inch spacing. Dividing by five gives 4 inches and leaves the last hole four inches short of where it belongs.
Why is it one fewer?
It is the fencepost problem: a fence with five posts has four panels between them. Counting the things rather than the spaces between them is one of the oldest arithmetic traps there is, and a placket is exactly that shape — two fixed ends with holes distributed between.
Does the error get worse with more buttonholes?
The opposite, which nobody expects. With eight holes over a 20 inch span the mistake costs two and a half inches; with four it costs five. The relative difference between n and n minus one grows as n shrinks, so the sparse plackets where a misplaced hole is most visible are also where the error is largest.
Where should the first buttonhole go?
About half a button width below the neckline seam, so the button sits clear of the edge rather than riding over it. On a collared shirt there is usually one on the collar band as well, which is placed relative to the band rather than counted in the placket spacing.
Where should a buttonhole go on a blouse?
One exactly at the bust point, and space the others around it. Gaping happens where the strain is, and a buttonhole placed there is what prevents it — working outward from that hole is far more effective than spacing evenly and hoping. The same argument puts one at the waist on a fitted coat.
Should the last one be at the hem?
Usually not. Ending three or four inches above the hem is normal and stops the front flaring open when you sit down. On a long coat the lowest button is often much higher again, so the skirt of the coat can move.
How long should the buttonhole be?
The button diameter plus its thickness plus about an eighth of an inch of ease. A hole cut to the diameter alone grips, because the button has to turn edgewise to pass through and its thickness then matters as much as its width. A thick shank or domed button needs noticeably more than a flat disc the same width.
Horizontal or vertical buttonholes?
Horizontal takes strain far better, because the button slides to the end of the hole and stays there under load. Vertical holes are used on narrow bands where there is no room to go across, and on plackets where no real strain is expected — they let the button travel along the hole, which is why a strained vertical buttonhole pops open.
How far in from the edge?
Half the button diameter plus the placket allowance, so the button sits fully on the placket rather than overhanging the finished edge. A button that hangs over the edge pulls the placket out of line every time it is done up.
How wide does the placket need to be?
At least the button diameter plus a quarter inch, so there is fabric on both sides of it. A placket exactly as wide as the button leaves the button touching both edges, which looks wrong and wears through the edge stitching. This page warns when the numbers you enter do not leave room.
How should I mark the positions?
From the top, every time. Measuring each gap from the previous mark accumulates every small error down the placket, so by the sixth hole you can be a quarter inch out with no single mistake to point at. Measuring each position from the same reference keeps errors independent rather than cumulative.
Does this send anything anywhere?
No. Everything is calculated in your browser and nothing is stored or uploaded.
🔒 This tool runs entirely in your browser. Nothing you enter is uploaded, logged, or stored.