How to use the binding calculator
- Pick a quilt size or type the finished width and length. Measure the quilted top before you trim it if you can, since quilting can shrink a top by an inch or two.
- Choose a strip width. The chips cover the usual widths for double-fold binding, and you can type anything else.
- Leave the extra length at 12 inches unless you know you like more tail to work with.
- Check the fabric width and selvage trim.
How the binding math works
Binding goes all the way around the quilt, so the starting point is the perimeter. The calculator adds a margin for the diagonal seams that join the strips, the overlap where the ends meet and the fold at each mitered corner.
Cut the strips across the fabric from selvage to selvage. Dividing the binding length by the usable width and rounding up gives the number of strips. Stacked together, those strips are the fabric you need, rounded up to the next eighth of a yard.
For continuous bias binding you cut one square, sew it into a tube with an offset seam and cut one long spiral strip. The area of fabric has to equal the binding length times the strip width, so the side of the square is the square root of that area. The calculator adds one strip width on top and rounds up to a whole inch.
Formulas
- Binding length = 2 × (width + length) + extra for joins.
- Strips = binding length ÷ (fabric width − selvage trim), rounded up.
- Yards = strips × strip width ÷ 36, rounded up to ⅛ yd.
- Folded width past the seam = strip width ÷ 2 − seam allowance.
- Bias square side = √(binding length × strip width) + strip width, rounded up to a whole inch.
Worked example: a queen quilt
The quilt is 90 by 95 inches. The perimeter is 2 × (90 + 95) = 370 inches, and 12 more for joins makes 382. Quilting cotton 42 inches wide gives 40 usable inches once you trim the selvages, so 382 ÷ 40 = 9.55, which rounds up to 10 strips.
Ten strips at 2½ inches is 25 inches of fabric. That is 0.69 yard, so buy ¾ yard. Each strip folds to 1¼ inches, and after a ¼ inch seam there is 1 inch left to wrap to the back.
For continuous bias, 382 × 2.5 = 955 square inches. The square root is about 30.9, plus 2.5 is 33.4, so cut a 34 inch square. That takes 1 yard of fabric.
Binding chart for standard quilt sizes
Straight-grain binding from 42 inch fabric with 12 inches extra. Bias squares are for 2½ inch strips. The 2¾ inch column is for thick, high-loft batting, where a wider strip still covers the stitching on the back.
| Size | Binding length | Strips | 2¼" strips | 2½" strips | 2¾" strips | Bias square |
|---|---|---|---|---|---|---|
| Crib 36" × 52" | 188" | 5 | ⅜ yd | ⅜ yd | ½ yd | 25" |
| Throw 50" × 65" | 242" | 7 | ½ yd | ½ yd | ⅝ yd | 28" |
| Twin 68" × 86" | 320" | 8 | ½ yd | ⅝ yd | ⅝ yd | 31" |
| Full 84" × 90" | 360" | 9 | ⅝ yd | ⅝ yd | ¾ yd | 33" |
| Queen 90" × 95" | 382" | 10 | ⅝ yd | ¾ yd | ⅞ yd | 34" |
| King 108" × 95" | 418" | 11 | ¾ yd | ⅞ yd | ⅞ yd | 35" |
Binding from fat quarters
You can cut binding from fat quarters or scraps when one fabric runs short. A fat quarter is about 18 by 21 inches once trimmed, so it gives 7 strips 2½ inches wide, each about 21 inches long. Scrappy binding needs the same total length, just in shorter pieces.
| Size | Binding length | Strips from 42" fabric | Strips from fat quarters | Fat quarters |
|---|---|---|---|---|
| Crib | 188" | 5 | 9 | 2 |
| Throw | 242" | 7 | 12 | 2 |
| Twin | 320" | 8 | 16 | 3 |
| Full | 360" | 9 | 18 | 3 |
| Queen | 382" | 10 | 19 | 3 |
| King | 418" | 11 | 20 | 3 |
Strips from fat quarters are about half as long, so you sew about twice as many joining seams. Cut along the 21 inch side to keep each strip as long as possible.
How much extra length to add
Published formulas don't agree on the extra length. Broadcloth Studio adds 10 inches to the perimeter. This calculator adds 12. On most sizes the choice changes the strip count by one at most, because the last strip usually has room to spare. The guide to binding a quilt has a table of strip counts for each allowance, and you can type any extra length into the calculator.
Bias or straight: the fabric difference
Bias binding takes more fabric than straight-grain binding, and the calculator shows that the ratio depends on the quilt size. A queen needs ¾ yard for straight strips and 1 yard for a continuous bias square, about 1.3 times as much. A crib quilt needs ⅜ yard straight and ¾ yard on the bias, 2.0 times as much, because even a small bias square takes a full-width cut as deep as the square. If you only bind straight edges, straight strips are the thrifty choice.
For a flange binding, which shows a narrow accent strip on the front, you sew two strips together lengthwise, one ¼ inch wider than the other. Run the calculator once for each strip width to get both fabrics.
Tips for binding
- Join strips with a diagonal seam and press it open. The bulk spreads out, so the seam is hard to spot on the finished edge.
- Trim the batting and backing even with the top before you sew the binding on, and measure the quilt again at that point.
- Use bias binding for curved edges, rounded corners or quilts that will get heavy use. The threads run at 45 degrees, so no single thread sits along the fold.
