Buttonhole Spacing Calculator
Calculates the even spacing between buttonholes along a garment placket given the placket length, number of buttons, and top and bottom margins. Use it when constructing shirts, coats, or any garment with a button band.
About this calculator
Evenly spaced buttonholes are essential for a professional-looking garment. The calculation treats the usable placket length — after subtracting the top and bottom margins — as the space that must be divided into equal intervals. The formula is: spacing = (placketLength − topMargin − bottomMargin) / (numberOfButtons − 1). You subtract 1 from the number of buttons because the first button sits at the top margin position and the last sits at the bottom margin position, leaving (n − 1) gaps between them. The button diameter is used separately to ensure the buttonhole length is correct (buttonhole length = button diameter + 0.125 inches ease), but it does not affect the spacing calculation. Mark the first buttonhole at topMargin from the top edge, then place subsequent ones every spacing inches down the placket.
How to use
A shirt placket is 14 inches long. You want 7 buttons, with a 0.75-inch top margin and a 0.75-inch bottom margin. Step 1 — usable length: 14 − 0.75 − 0.75 = 12.5 inches. Step 2 — number of gaps: 7 − 1 = 6. Step 3 — spacing: 12.5 / 6 ≈ 2.083 inches between each buttonhole. Step 4 — mark positions from the top: 0.75", 2.83", 4.92", 7.00", 9.08", 11.17", 13.25" (which equals placketLength − bottomMargin = 13.25"). All seven buttonholes are evenly distributed with identical gaps.
Frequently asked questions
How do I calculate even buttonhole spacing on a shirt placket?
Measure the total placket length, decide on the margins you want at the top and bottom edges, then divide the remaining length by one fewer than the number of buttons. The formula spacing = (placketLength − topMargin − bottomMargin) / (numberOfButtons − 1) gives you the distance between buttonhole centers. Mark the first buttonhole at the top margin, then step down by the spacing value for each subsequent button. Using a quilting ruler or a seam gauge makes transferring these measurements to fabric quick and accurate.
What size should a buttonhole be relative to the button diameter?
A buttonhole should be the diameter of the button plus approximately 0.125 inches (3 mm) of ease so the button passes through smoothly without stressing the fabric. For thick or dimensional buttons — shanks, toggles, or covered buttons — add a little more ease, up to 0.25 inches. The buttonhole length is measured along the cut opening, not the finished bartacked end. Always test a buttonhole on a scrap of your fashion fabric and interfacing before sewing them on the actual garment, since stitch length and tension vary by machine and fabric.
Why do I subtract 1 from the number of buttons when calculating spacing?
When you place buttons along a line, the first button occupies the top margin position and the last button occupies the bottom margin position. Between n buttons there are exactly n − 1 gaps. If you divided by n instead of n − 1, you would create one extra gap and the last button would land short of the bottom margin, leaving the placket unbalanced. This off-by-one relationship appears in any equally-spaced placement problem — fence posts, shelf brackets, or stair balusters — and is one of the most common measurement errors in garment construction.