Buying fabric is a puzzle: pieces have to fit across the width of the bolt, and every inch of length is paid for. This calculator lays identical rectangles in rows across the fabric to find the length to buy, with seam allowance and shrinkage included.
Fabric width
Fabric is sold by length from bolts of a fixed width:
- 44/45 in: quilting cotton and many apparel cottons;
- 54 in: home decor fabrics for curtains and cushions;
- 58 to 60 in: many knits, linen and apparel fabrics.
The edges, or selvages, are tightly woven and printed with the maker’s name. Most sewists trim them off, so the usable width is about 1 in less than the label.
How the layout works
- Add the seam allowance to each side of the finished piece: an 18 × 24 in piece with ½ in seams is cut at 19 × 25 in.
- Count how many cut widths fit across the usable width: floor((44 − 1) ÷ 19) = 2 pieces per row.
- Count the rows: 6 pieces ÷ 2 = 3 rows.
- Multiply rows by cut length: 3 × 25 = 75 in.
- Add shrinkage: cotton can shrink 3 to 5% when prewashed, so 75 × 1.05 = 78.75 in.
- Convert to yards (36 in each) and round up to the next ⅛ yard: 78.75 ÷ 36 = 2.19, so buy 2¼ yards.
If a piece is wider than the fabric, the calculator warns you: rotate it, choose a wider fabric or plan a seam.
When to buy extra
The calculator assumes plain fabric and pieces cut in the same direction. Add more when:
- the print has a one-way design or a nap (velvet, corduroy), so pieces cannot be turned;
- you need to match a pattern at the seams, such as stripes, plaids or large repeats (add one repeat per length);
- the store may cut slightly crooked, which is common;
- it is your first time with the pattern and a mistake is possible.
A safety margin of 10% or ⅛ to ¼ yard is cheap insurance.
Prewashing
Wash and dry fabric the way the finished item will be washed, before you cut. Shrinkage is highest in cottons, linens and rayon; polyester barely shrinks.