How wide should a button placket be?

Standard shirt plackets are 2.5–3.5cm wide when finished. Dress plackets are often 2–2.5cm. The placket width should be proportional to the button size — the button should sit centred on the placket with at least 3mm clearance either side.

How do I calculate button spacing?

Divide the distance between the first and last button positions by the number of gaps (buttons minus one). For a 45cm opening with 6 buttons, leaving 2cm top and bottom: (45 - 4) ÷ 5 = 8.2cm between each button.

What size should buttonholes be?

The standard buttonhole length is the button diameter plus 3mm. For thick or domed buttons, add the button thickness as well. Always sew a test buttonhole on scrap fabric first to check the fit.

Do I need interfacing on a placket?

Yes, almost always. Interfacing prevents the placket from stretching and gives it a crisp, professional finish. Use medium-weight fusible woven interfacing for most fabrics. Lightweight interfacing suits delicate fabrics like lawn or voile.

SewCalcs

Placket Calculator — Button Placket Dimensions

Calculate button placket dimensions and button spacing for shirts, blouses and dresses.

Placket Length

Total length of the button placket

Finished Placket Width

Finished visible width of one side

Number of Buttons

Total buttons on the placket

Button Diameter

Diameter of each button

Placket StyleConstruction method for the placket

How We Calculate This

This calculator works out placket cut dimensions, button spacing and buttonhole length based on your placket style and button details.

Placket styles

Separate band: Cut width = (placket width × 2) + (seam allowance × 2). Two pieces needed.
Folded-back: Cut width = (placket width × 2) + seam allowance + 1cm turn. Built into front piece.
Concealed: Like separate but with extra 1cm underlap for the fly front.

Button spacing

Spacing = (Placket length − top distance − bottom distance) ÷ (button count − 1)

Frequently Asked Questions

Related Calculators

Waistband Calculator

Calculate fabric cut size, interfacing dimensions, elastic length and notions for any waistband type.

Sleeve Ease Calculator

Calculate sleeve cap ease based on armhole measurement, garment style and fabric type.

Lining Calculator

Calculate lining fabric needed from shell pattern measurements and garment type.

Last updated: March 2026

All calculations are estimates. Always verify quantities before cutting or purchasing fabric.