Quick answer: how to calculate bias binding
Edge length equals 2 times finished width plus 2 times finished length for a rectangle, or the measured length around the edge for a curved quilt. Bias length needed equals edge length plus extra. Strips are rounded up, and yardage to buy is exact yardage rounded up to the nearest 1/8 yard, never down.
Example: total edge length measured at 400 inches, strip width 2.5 inches, usable fabric width 44 inches, seam 0.5 inch, extra 15 inches. Bias length needed is 415 inches, strips are 10, exact yardage is 0.69 yards, yardage to buy is 0.75 yards.
This guide and its calculator work by strips, not by a single square. If you want one long continuous bias strip from a single square, use the Continuous Bias Binding Calculator, which gives a square size. Do not expect a square size from this strip calculator, and do not expect strip yardage from the square calculator, because they answer different questions.
Fabric width means usable width after removing selvages, not bolt width. Extra is 15 inches by default for bias, a little more than straight binding, because bias needs gentler handling, joins, curves, and final overlap. Measure after quilting, and measure a curved edge directly with a flexible tape, without stretching.
If you only need a number, use the Bias Binding Calculator. If you want to understand why that number is right, and when to use continuous bias instead, read on.
What bias binding is
Bias binding is binding cut on the bias, at 45 degrees to the grain of the fabric. Because the cut is diagonal, the strip can stretch a little, and it can bend around curves, scallops and round edges without puckering. That stretch is the whole point of bias binding, and it is also the thing you must handle carefully, because bias fabric stretches when you do not want it to, as well as when you do.
Bias binding is still binding. It wraps the raw edge of the quilt sandwich after quilting, just like straight grain binding. The difference is in the cut, and in the edges it suits, not in the job it does at the edge.
When bias binding is needed, and when it is not
| Use bias binding | Straight grain binding is enough |
|---|---|
| Curved edges, scallops, and round or oval quilts | Straight edges, square corners, most rectangular quilts |
| Edges that bend in more than one direction | Edges that run straight from corner to corner |
| Striped fabric where the stripe should run diagonally around a curve | Striped fabric on a straight edge, where grain direction is clear |
Bias binding can be used on straight edges too, but it is not needed there, and it needs gentler handling than straight grain binding. Use bias where the edge bends, and straight grain where it does not, unless you have a design reason to do otherwise.
How to measure a curved edge
For a rectangle quilt, edge length is 2 times width plus 2 times length. For a curved quilt, that formula does not work, because the edge is not a rectangle. Measure around the edge directly, with a flexible tape, following the edge closely, without stretching the quilt or the tape.
- Measure after borders and quilting, because binding goes around the finished edge.
- Measure twice, and use the larger number if measurements differ, so binding does not come up short on a curve.
- For a round quilt, you can also check measurement against circumference, which is pi times diameter, but direct measurement around the edge is more reliable for a quilt that is not a perfect circle.
- Write the measurement down before calculating, because a curved edge is easy to misremember, and a wrong edge length gives wrong yardage.
Step by step: how to calculate bias binding
Step 1: Get total edge length
For a rectangle, edge length equals 2 times finished width plus 2 times finished length. For a curved, scalloped or round quilt, edge length is the total length you measure around the edge. Use finished size or measured edge length, after borders are added.
Step 2: Add extra for joins, curves and overlap
Bias length needed equals edge length plus extra. Extra covers joining strips, easing around curves, and the final overlap where binding ends meet. The calculator default is 15 inches for bias binding, a little more than straight binding, because bias needs gentler handling. Change it if your method needs more or less.
Step 3: Work out strips needed
If bias length needed fits in one fabric width, you need 1 strip. If not, each extra strip adds fabric width minus seam allowance, because seam allowance is lost at each join. Strips are rounded up. A part strip still needs a full strip of fabric.
Step 4: Convert strips to yardage
Fabric length to buy equals strips times binding strip width, because each strip is binding strip width wide. Divide fabric length by 36 to get exact yardage in inch mode. Round up to the nearest 1/8 yard. Rounding up covers cutting and trimming, and it is not waste.
Try it with the calculator: Use the Bias Binding Calculator with your own edge length or finished quilt size, binding strip width and fabric width. It uses the same steps as this guide, and it shows edge length, bias length needed, strips needed and yardage together.
Worked example: a quilt with a long curved edge
Take a quilt with total edge length measured at 400 inches. Use binding strip width 2.5 inches, fabric width 44 inches, seam allowance 0.5 inch, extra 15 inches.
Edge length: 400 inches, measured around the edge, without stretching the quilt.
Bias length needed: 400 plus 15 equals 415 inches.
Strips needed: 415 inches does not fit in 44 inches. Each extra strip adds 43.5 inches. Strips equal 1 plus the ceiling of (415 minus 44) divided by 43.5, which is 10 strips.
Fabric length to buy: 10 times 2.5 equals 25 inches. Exact yardage: 25 divided by 36 equals 0.69 yards. Yardage to buy, rounded up to the nearest 1/8 yard, equals 0.75 yards.
Bias binding yardage table, our own computed table
This table uses finished quilt size for a rectangle, strip width 2.5 inches, usable fabric width 44 inches, seam 0.5 inch, and extra 15 inches, and it is computed from the same strip rule as the calculator, not copied from another site. For a curved quilt, use measured edge length in the calculator instead of a table row, because a table cannot know your curve.
| Finished quilt size | Edge length | Bias needed | Strips | Yardage to buy |
|---|---|---|---|---|
| Baby 36 by 48 in | 168 in | 183 in | 5 | 0.38 yards |
| Lap 50 by 60 in | 220 in | 235 in | 6 | 0.50 yards |
| Twin 68 by 88 in | 312 in | 327 in | 8 | 0.63 yards |
| Full 80 by 92 in | 344 in | 359 in | 9 | 0.63 yards |
| Queen 90 by 108 in | 396 in | 411 in | 10 | 0.75 yards |
| King 108 by 108 in | 432 in | 447 in | 11 | 0.88 yards |
How to make sure your result is correct
- Edge length check. For a rectangle, edge length must equal 2 times finished width plus 2 times finished length. For a curve, it must be a direct measurement, not a rectangle estimate.
- Extra check. Bias needed must equal edge length plus extra, and extra must cover joins, curves, and final overlap.
- Strips check. Strips must be rounded up, and each extra strip must add usable width minus seam allowance, not full bolt width.
- Buy versus exact check. Buy yardage must never be below exact yardage. If it is, you rounded the wrong way.
- Method check. If you need a single square, you are in the wrong calculator. Use the Continuous Bias Binding Calculator for a square, and this calculator for strips.
- Stretch check. If bias was stretched while measuring, the measurement is too long, not too short, and the finished edge can wave. Measure without stretching, and ease, never pull, around curves.
Cutting and handling bias strips
- Cut bias strips at 45 degrees to the grain, at the strip width you calculated for. Press fabric flat before cutting, so the diagonal stays true.
- Join strips end to end with a diagonal join, and press seams open, so joins lie flat and do not bulk up on a curve.
- Handle bias strips gently. Do not pull or stretch them while cutting, joining or sewing, or the finished edge will wave.
- Ease bias binding around curves, instead of pulling it straight. Small, even easing gives a smooth curve, while pulling gives puckers.
- Check the edge after sewing, before finishing the back, so a stretched section can be eased back while it is still easy to fix.
This is a summary, not a full bias binding tutorial. If you have never cut bias binding, cut and join a few strips on scrap fabric first, and practice easing them around a curved sample, before cutting into your binding fabric.
Common mistakes with bias binding
- Using straight grain binding on a curve. Straight grain will not stretch around a curve without puckering. Use bias for curves.
- Measuring a curved edge as a rectangle. A rectangle perimeter undermeasures a scalloped or round edge. Measure around the edge directly.
- Stretching bias while measuring or sewing. Bias stretches easily, so a stretched measurement gives yardage that is too short, and a stretched seam gives a wavy edge.
- Forgetting extra length. Joins, curves and final overlap need extra length, and the calculator default is 15 inches for bias for that reason.
- Rounding yardage down. Rounding down can leave you a few inches short at the end of a strip, when the quilt is already quilted and hardest to fix.
Calculate your own bias binding now
Use your edge length or finished quilt size, binding strip width and fabric width in the calculator, and check the result against the steps in this guide.
Open the Bias Binding CalculatorFrequently asked questions
Yes, bias binding works on straight edges, but it is not needed there, and it needs gentler handling than straight grain binding. Use bias where the edge bends, and straight grain where it does not, unless you have a design reason to use bias throughout.
It can, depending on how bias strips are cut. Cutting bias strips from yardage can waste more fabric at the corners of the cut than cutting straight strips. Continuous bias binding, cut from a single square, can be more efficient. For yardage by strip count, use the calculator above, and for a single square, use the Continuous Bias Binding Calculator.
Cut at 45 degrees to the grain, at the strip width you calculated for. Press fabric flat first, mark the diagonal carefully, and cut without stretching the fabric. Join strips with a diagonal join, and press seams open, so joins lie flat.
Usually because bias was stretched while cutting, joining or sewing, or because it was pulled straight around a curve instead of eased. Handle bias gently, ease around curves in small amounts, and check the edge before finishing the back.
This guide is about calculating bias binding, with edge length, strips and yardage. The Bias vs Straight-Grain Binding guide is a comparison of the two types, to help you choose which one suits your quilt edge. Read both if you are deciding, and use this guide for the numbers.
Related guides and calculators
Next, read Bias vs. Straight-Grain Binding to compare bias and straight grain, and use the Continuous Bias Binding Calculator if you want one long bias strip from a single square. For straight edges, see the Binding Calculator, and for the back of the quilt, see How to Calculate Backing.