Sewing calculators: stitch length, cut size, pillow covers, yardage and buttonholes

Five small calculators for the numbers the chapters ask for: stitch length in millimeters or stitches per inch, cut sizes from finished sizes, an envelope pillow cover, yardage at another fabric width, and buttonhole and shank length. Pre-filled from your setup.

Stitch length: millimeters and stitches per inch

Most current machines set stitch length in millimeters; older guides and many patterns give stitches per inch (SPI). Enter either one. Stitching and tension explains stitch length and how to count it.

Ranges the sources give

Assumptions

• Stitches per inch = 25.4 ÷ stitch length in mm, because the inch is exactly 25.4 mm (NIST, SI units of length). Physical principle
• The ranges are conventions from the sources named, written for their own machines and fabrics. They differ, and a sample on two layers of the real fabric decides. Convention Test it
• Some machines label the dial with numbers that are not millimeters. The manual says what the numbers mean. Product-specific

Cut size from finished size

For any rectangle: a napkin, a bag body, a strap, a skirt panel. Enter the size you want once it is sewn, and the seam allowance the project uses. Leave the top and bottom allowances blank to use the seam allowance there too, or enter a hem or casing allowance. Cutting, marking and pressing explains it.

Assumptions

• Cut width = finished width + 2 × seam allowance. Utah State University Extension's Four Square Pillow works it the same way: 1/2 in seams turn a 15 in front into a 14 in finished cover. Convention
• Seam allowances differ by project and pattern family: 5/8 in in US commercial patterns, 1/2 in in many flat projects, 1/4 in in quilting (Seams and a first piece). Use the project's own figure.
• The fabric estimate lays identical pieces in rows across the width you enter. It ignores grain direction, one-way prints and nap, and does not add fabric for squaring the ends. Enter the width you measured after preshrinking, and the lengthwise shrinkage from your shrink test if you have not preshrunk yet. Utah State's skirt instructions add 1/4 yd for shrinkage and straightening; that is one source's margin, not a rule. Test it

Envelope pillow cover

A front and two overlapping backs, with no zipper. Measure the pillow form across the middle, seam to seam: Utah State's Reversible 18" Tied Pillow says to measure before you buy, because labels vary. Your project sews it.

Assumptions

• Front = form + 2 × seam allowance each way, so the finished cover is the form's own size and fits snugly. That is Utah State's convention in both pillow projects; its tied pillow says the cover should fit snugly. A looser cover needs a larger front. Convention
• Each back = half the front's cut width + half the overlap + the hem allowance on its opening edge, the same height as the front.
• The 4 in overlap and the 1 in hem (1/2 in turned twice) are our assumptions. No source we fetched gives an overlap figure. Utah State's Four Square Pillow cuts two 9 1/2 × 15 in backs for a 15 in front and closes them with 3 in of hook-and-loop tape, which works out to about 2 in of overlap if each opening edge takes a 1 in hem. A larger overlap gaps less on a sofa cushion that gets leaned on; the try with the form settles it. Preference
• The fabric estimate packs the front and backs, which share one height, into rows across the usable width, largest first. It ignores one-way prints; a directional print may need every piece the same way up.

Yardage at another fabric width

A pattern envelope lists yardage for each size at one or two fabric widths, often 45 in and 60 in. When your fabric is narrower or wider and the chart does not list it, this scales the figure. Patterns and fit reads the chart.

Assumptions

• Approximate yards = envelope yards × envelope width ÷ your width, rounded up to the next 1/8 yd. This keeps the area the same. Real layouts do not scale evenly: a piece that fit across 45 in may not fit across 42 in at all. Width-conversion charts that circulate among fabric shops differ from simple scaling by several percent in either direction, and we found no original to cite, so we do not reproduce one. Convention
• Simplicity's guide to understanding the pattern envelope notes that narrower fabric needs more yardage, and that fabric with a nap or one-way design needs the "with nap" figure. The envelope's figure at your actual width wins over this calculator. Product-specific

Buttonhole and thread shank

Buy the buttons first. Measure the button across its widest point and through its thickness; for a dome or shank button, wrap a strip of paper or tape around its widest part instead. For a sewn-on button, also measure the garment's thickness at the buttonhole, all layers. Closures and elastic sews the test buttonhole; Everyday mending sews the button.

Assumptions

• Buttonhole = diameter + thickness, from the University of Idaho's Machine Buttonholes and Buttons (1983) and the sewing.org buttonhole lesson, which calls it a general rule. Convention
• The CAERT unit hosted by the Illinois State Board of Education adds 1/8 in for fabric thickness. NMSU's Guide C-231 takes half the wrap measurement plus 1/8 in, which suits buttons that are not flat. All three are starting points; NMSU and sewing.org both say to test. Test it
• Thread shank = garment thickness + 1/16 in (University of Idaho) or + 1/8 in (University of Tennessee 4-H, Repair Your Clothes). Shown to the nearest 1/16 in. Convention

See it with the fictional cases

Write each result in the cut list and the settings that worked in the stitch sample log. The fit calculators cover ease and an elastic-waist skirt.