The standards of a well-made buttonhole are:
Width is appropriate to the weight of the fabric and size of the buttonhole.
Ends are bar-tacked to prevent buttonhole from tearing under stress.
Stitches are evenly spaced on each side of the buttonhole.
Buttonhole is 1/8" (3 mm) longer than the button.
Stitches on each side are far enough apart so that the buttonhole can be cut open without cutting the stitches.
Ends have not been cut open accidentally.
Interfacing supporting the buttonhole matches the fashion fabric and is not obvious on the cut edges.
Buttonhole is on-grain; vertical buttonholes are perfectly parallel to the garment edge, horizontal buttonholes are at perfect right angles to the edge.
Horizontal buttonholes are the most secure, because they are not as apt to let buttons slip out. These buttonholes also absorb any pull against the closure with little, if any, distortion. Horizontal buttonholes should extend 1/8" (3 mm) beyond the button placement line, toward the edge of the garment. Be sure that the space from the center line to the finished edge of the garment is at least three-fourths the diameter of the button. With this spacing, the button will not extend beyond the edge when the garment is buttoned.
Vertical buttonholes are used on plackets and shirt bands. These are usually used with more and smaller buttons to help keep the closure secure. Vertical buttonholes are placed directly on the center front or center back line.
When a garment is buttoned, the button placement lines and center lines of both sides must match perfectly. If the overlap is more or less than the pattern indicates, the garment may not fit properly.
Spaces between buttonholes are generally equal. You may have to change the pattern buttonhole spacing if you have made pattern alterations that change the length or alter the bustline. Respacing may also be necessary if you have chosen buttons that are larger or smaller than the pattern indicates. Buttonholes should be spaced so they occur in the areas of greatest stress. When they are incorrectly spaced, the closing gaps and spoils the garment’s appearance.
For front openings, place buttonholes at the neck and the fullest part of the bust. Place a buttonhole at the waist for coats, overblouses and princess-seamed dresses or jackets. To reduce bulk, do not place a buttonhole at the waistline of a tucked-in blouse or belted dress. Buttons and buttonholes should end about 5" to 6" (12.5 to 15 cm) above the hemline of a dress, skirt, or coatdress.
To evenly respace buttonholes, mark the locations of the top and bottom buttons. Measure the distance between them. Divide that measurement by one less than the number of buttons to be used. The result is the distance between buttonholes. After marking, try on the garment, making sure the buttonholes are placed correctly. Adjust as necessary.