Measure the perimeter first
For a rectangular 60 × 80-inch quilt, the perimeter is 280 inches. Add 12 inches for tails and the final join to make a 292-inch target. Choose the extra length for your own joining method; the default is not a promise that every technique needs the same allowance.
Account for diagonal strip joins
Joining straight-grain strips diagonally reduces their combined length. This model deducts one strip width for each join between strips. Eight 42-inch strips cut 2½ inches wide provide 336 − 17.5 = 318.5 inches after seven joins, enough for the 292-inch target.
Convert strips to yardage
Eight strips at 2½ inches use 20 inches along the fabric, or about 0.56 yard. Rounded to quarter-yard increments, buy at least 0.75 yard before extra allowances. The result assumes every strip spans the usable width you entered.
Know when another method is needed
This is not a continuous bias-binding calculator. It does not model curved edges, scallops, irregular shapes or a pieced binding colour plan. Shrinkage, squaring and unusable fabric can reduce the yield. Check the cut list against your technique before cutting.
Questions, answered
Does strip width mean finished binding width?
No. Enter the full width of the strip before folding and sewing.
Why do I need more than perimeter divided by fabric width?
You also need joining tails, and each diagonal strip join consumes some length.