Quilting cotton is sold by length off a bolt that is about 44 in wide, of which 42 in is usable once the selvedges are trimmed. Yardage is therefore a question of how many strips of a given width you need to cut across that 42 in.
The method
- For each fabric, list every piece to cut and its cut size (finished size plus 1/2 in for squares, plus 7/8 in for half-square triangle squares).
- Work out how many pieces fit across one 42 in strip: 42 divided by the cut size, rounded down. A 2.5 in square fits 16 to a strip.
- Divide the piece count by that and round up to get the number of strips.
- Multiply strips by cut width for the inches of fabric, add 8% for squaring up and shrinkage, and round up to the next 1/8 yard.
The yardage calculator and every generated pattern do exactly this and print the strip counts, so you can also use the table as your cutting plan.
Borders and binding
Border strips are cut across the width of fabric and joined, so a border needs enough strips to cover twice the width plus twice the height plus a little for the joins. Binding is cut at 2.5 in and needs the perimeter plus about 10 in.
Backing and batting
Backing should be about 4 in larger than the top on every side. If the top is 34 in wide or less it fits on one width of fabric; wider tops need two lengths seamed, or a wide backing fabric (108 in). Batting comes in packaged bed sizes; buy the one that is at least 8 in larger than the top each way.
Precuts
Precut bundles skip the strip math. A charm pack of 42 five-inch squares makes a 6 by 7 layout that finishes at 27 by 31.5 in; a jelly roll's 40 strips at 2.5 in cover a throw. The precut database lists sizes and typical counts.