Quilt Continuous Bias Binding Calculator: One Long Bias Strip from a Square
Work out continuous bias binding before you cut. Enter binding length and strip width, and see the square size, yield and yardage to buy, with the formula in steps.
Calculate your continuous bias binding
Needed bias length is edge length plus extra for joins, curves and overlap. For a rectangle, edge length is 2 times width plus 2 times length. For a curved quilt, measure around the edge directly.
Waste allowance is added to needed bias length before the square is worked out, to cover cutting and handling loss. Choose 0% for the base calculation with no waste.
Fabric square side is the side length of the square you will cut bias from, before sewing it into a tube.
Binding strip width is the cut width of each bias strip, not the finished width on the quilt edge. A common cut width for double fold binding is 2.5 inches.
This calculator works out continuous bias binding from a single fabric square. For regular bias strips joined together, use the Bias Binding Calculator. For straight edges with straight grain binding, use the Binding Calculator.
Enter your measurements, then calculate.
| Square side needed | |
| Continuous bias length | |
| Base square side, no waste | |
| Base bias length, no waste | |
| Waste allowance | |
| Fabric length to buy | |
| Exact yardage | |
| Yardage to buy |
How the calculator works
Step 1: Square side needed
Square side needed equals the square root of needed bias length times binding strip width, after waste allowance is added to needed length. Needed bias length is edge length plus extra for joins, curves and overlap. Waste allowance is optional: with the default 10 percent, a needed length of 335 inches becomes 368.5 inches before the square is worked out. With 0 percent waste, the base square is used unchanged. For example, with no waste, if needed length is 335 inches and strip width is 2.5 inches, square side needed is the square root of 335 times 2.5, which is 28.94 inches.
Step 2: Round square side up
Square side is rounded up to the nearest 0.5 inch, for practical cutting. In the no-waste example, 28.94 inches rounds up to 29.0 inches. Rounding up gives a little extra bias length, which is safer than rounding down. Waste allowance is separate from this rounding, and it is shown separately in the result, so the same extra is never counted twice.
Step 3: Continuous bias length from the square
Continuous bias length equals square side squared divided by binding strip width. In the example, 29 squared divided by 2.5 equals 336.4 inches, which covers needed length of 335 inches. If the square is too small, the calculator will show that the yield does not cover needed length, and you should use a larger square.
Step 4: Yardage
If square side fits in fabric width, fabric length to buy equals square side, because you need one square piece. Exact yardage equals fabric length divided by 36 in inch mode. Yardage to buy is exact yardage rounded up to the nearest 1/8 yard. In centimetre mode, metres to buy are rounded up to the nearest 0.1 metre. The unit toggle changes all inputs, outputs and rounding together.
Assumptions, shown next to the result
This is the standard area method for continuous bias, and actual yield varies a little with seam allowances at tube joins and with cutting. The calculator rounds square side up to cover that variation, but it does not add a separate seam allowance to the formula, because tube seams are part of the continuous cutting method, not strip joins. Waste allowance, when you choose it, is added to needed length before the square is worked out, and the base result without waste is shown beside it. If square side exceeds fabric width, a single square cannot be cut from that fabric width. The calculator warns you in that case, instead of giving a misleading yardage. Piece a square, choose a wider fabric, or use regular bias binding instead.
Continuous bias and regular bias are different
Regular bias binding joins many short bias strips together. Continuous bias binding sews a square into a tube, offset by one strip, and cuts it in a spiral, so you get one long strip with far fewer joins. Continuous bias needs a square piece of fabric. Regular bias can be cut from yardage. Use the Bias Binding Calculator for regular bias strips.
Square size chart by quilt size
This chart uses the same formula as the calculator: binding strip width 2.5 inches, 44 inch fabric, needed bias length from the bias chart, which is edge length plus 15 inches extra, square side rounded up to the nearest 0.5 inch, yardage rounded up to the nearest 1/8 yard.
| Quilt size | Needed bias length | Square side needed | Bias length you get | Yardage to buy |
|---|---|---|---|---|
| Baby | 215 in | 23.5 in | 220.9 in | 0.75 yards |
| Lap | 267 in | 26.0 in | 270.4 in | 0.75 yards |
| Twin | 359 in | 30.0 in | 360.0 in | 0.88 yards |
| Full | 391 in | 31.5 in | 396.9 in | 0.88 yards |
| Queen | 443 in | 33.5 in | 448.9 in | 1.00 yard |
| King | 479 in | 35.0 in | 490.0 in | 1.00 yard |
Chart yardage is a guide for the sizes shown. Continuous bias yardage is a little higher than regular bias yardage for the same quilt, because you must buy a full square piece. You gain one long continuous strip with far fewer joins. Use the calculator above for your own needed length and strip width.
Worked example, checked against the calculator
Needed bias length 335 inches, binding strip width 2.5 inches, fabric width 44 inches.
Square side needed: square root of 335 times 2.5 equals square root of 837.5, which is 28.94 inches. Rounded up to the nearest 0.5 inch, square side needed is 29.0 inches.
Continuous bias length you get: 29 squared divided by 2.5 equals 841 divided by 2.5, which is 336.4 inches. This covers needed length of 335 inches.
Fabric length to buy: square side 29 inches, which fits in fabric width 44 inches, so fabric length to buy is 29 inches. Exact yardage: 29 divided by 36 equals 0.81 yards. Yardage to buy, rounded up to the nearest 1/8 yard, equals 0.88 yards.
Reverse check: a 29 inch square, with strip width 2.5 inches, gives 336.4 inches of continuous bias, which matches the forward calculation. With the default 10 percent waste allowance, needed length becomes 368.5 inches, square side becomes 30.5 inches, continuous bias length becomes 372.1 inches, and yardage to buy stays 0.88 yards in this example. The base square without waste, 29 inches, is still shown in the result, so you can compare the two.
Frequently asked questions
How do I calculate continuous bias binding?
Square side needed equals the square root of needed bias length times binding strip width, after any waste allowance you choose is added to needed length, rounded up to the nearest half inch. The result also shows the base square without waste. Continuous bias length from a square equals square side squared divided by binding strip width.
How much fabric do I need for continuous bias binding?
You need a fabric square of the calculated side length. If square side fits in fabric width, fabric length to buy equals square side. Yardage equals square side divided by 36, rounded up to the nearest eighth yard.
What is the difference between continuous bias and regular bias binding?
Regular bias binding joins many short bias strips together. Continuous bias binding cuts one long spiral strip from a single fabric square, joined into a tube first, so there are far fewer joins. Continuous bias needs a square piece of fabric, while regular bias can be cut from yardage.
What if the square side is larger than fabric width?
Then a single square cannot be cut from that fabric width. Piece a square from two pieces, choose a wider fabric, or use regular bias binding instead. This calculator warns you when square side exceeds fabric width, instead of giving a misleading yardage.
Why is continuous bias yardage sometimes higher than regular bias yardage?
Because you must buy a full square piece, and cutting a square from yardage leaves unused fabric at the sides. You gain one long continuous strip with far fewer joins, but you may pay a little more in fabric for that convenience.
Can I use continuous bias for straight edges?
Yes, continuous bias works on straight edges too, but it is most useful for curved edges, where bias stretch matters, and for long bindings, where fewer joins matter. For a short straight edge, regular straight grain binding is simpler.
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