Binding Calculator

How the binding math works

Binding wraps the whole outside edge of your quilt, so you start with the perimeter — twice the width plus twice the length. Then we add about 10 inches: a little for each mitred corner and a little for the diagonal seam that closes the loop.

A worked example: a 60″ × 72″ throw

Take a common lap size, cut 2½″ double-fold binding from 40″ usable width of fabric. Those are this calculator's starting numbers, so you can follow along:

Notice the rounding happens at the strip count, not the inches. Six strips would give you 240″ — thirty-four inches short, which you would not discover until the binding was already on three sides of the quilt.

Where the 10 inches goes

It is an allowance, not a precise figure. Each mitred corner eats a small amount of length as the binding turns, and the diagonal seam that joins the two loose ends consumes roughly the width of the strip again. Ten inches covers four corners plus the closing join on a normal quilt with a little left over. On a quilt with many corners — a scalloped or stepped edge — add more, because every turn costs length.

Why diagonal seams

Joining binding strips on the diagonal spreads the bulk of the seam across a 45° line so it never lands as a hard lump on the edge of the quilt. A straight join stacks four layers of fabric in one place, and you will feel it under the needle and see it on the finished edge. The calculator's 10″ allowance assumes diagonal joins. See the full join walk-through if you haven't done one before.

Common mistakes

Measuring the pattern rather than the quilt. Quilts shrink slightly as they are pieced and quilted; measure the actual finished top. Forgetting that binding is cut across the width of fabric. The calculator gives strips × width of fabric, so a directional print will run sideways along the edge. Using selvage-to-selvage width as usable width. Trim the selvages first — 42″ of fabric is often only 40″ once they are gone, which is why 40 is the default here. Cutting bias binding using these numbers. Bias uses noticeably more fabric; see bias vs. straight grain.

Common questions

How wide should I cut my binding?

2½″ is the most common double-fold width and the default here. 2¼″ gives a slimmer finished edge, 2″ is snug and suits thin batting. The trade-off is covered in how wide should binding be — and note that going from 2¼″ to 2¾″ is more than a 20% jump in yardage, because every strip is cut the full width of fabric.

Do I need bias binding?

Only for curved or scalloped edges, where straight-grain binding cannot stretch around the curve. For a straight-edged quilt, straight-grain is stronger along the edge and uses less fabric.

Why did the calculator round my yardage up so far?

Fabric is sold in ⅛-yard steps, so the result rounds up to the next one you can actually buy. 17½″ of fabric is half a yard plus a hair, and a half yard (18″) covers it.