Continuous Bias Binding Calculator
Enter your project measurements and strip width to plan a continuous-bias starting square, check it against your fabric width, and see whether a scrap square is large enough.
Minimum fabric square side (in)25.5
- Binding length before waste (in)
- 228
- Planned cut-strip length (in)
- 250.8
- Fabric length to buy (yd)
- 0.71
- Square fits fabric width
- Yes — the 25.500 in square fits within the usable width.
- Theoretical binding from available square (in)
- 160
- Planned usable binding from available square (in)
- 145.45
- Available-square surplus or shortage (in)
- -82.55
Area planning assumes a single continuous-bias square and does not subtract seam, trimming, or marking losses beyond the waste allowance.
How to use this calculator
- Choose inches or centimeters, then use that same unit for every measurement.
- Enter the rectangular project dimensions, any extra binding length, and an allowance for joining the ends.
- Enter the strip cut width your pattern calls for, then choose a waste allowance and a practical rounding increment.
- Compare the rounded square with your usable fabric width before relying on the purchase estimate.
- Enter a scrap-square side to compare its planned usable yield with the binding length you need.
How to calculate continuous bias binding from a square
Continuous bias binding begins with a fabric square, which is cut and sewn into a loop before parallel bias lines are cut into one long strip. The useful planning relationship is area: the square has to supply the area of every strip before practical cutting losses. This calculator starts with the perimeter of a rectangular project, then adds any known straight sections and the extra length needed to join and position the binding.
The formulas are:
R = 2L + 2W + A + O
G = R x (1 + q / 100)
S = ceil(sqrt(G x C) / I) x I
- R is the binding length before waste.
- L and W are the outside project length and width.
- A is additional straight length, and O is joining and overlap allowance.
- G is the planned gross strip length after waste.
- C is the full bias strip cut width, q is the waste percentage, and I is the rounding increment.
- S is the rounded side of the starting square.
The square formula works because a square with side S has area S x S, while a strip run needs area G x C. The calculator rounds upward, so the actual area normally gives slightly more than the planned gross strip length. It also divides a scrap square's area by the strip width to show theoretical yield, then removes the selected waste percentage to give a more useful planned yield.
What moves the answer most
Project perimeter and strip width have a direct effect on the square. Doubling either one doubles required strip area, but the square side increases by the square root of that area. A wider strip needs more fabric for the same binding length. Waste and overlap allowance matter most on small projects, where a few added inches can be a meaningful share of the total.
Always compare the rounded square side with usable fabric width, not the width printed on the bolt. Selvages, damage, and prewashed shrinkage reduce the usable width. If the square is wider than the fabric, a single unpieced continuous-bias square cannot be cut from that width, so the purchase figure is intentionally withheld as a one-piece plan.
What this calculator leaves out
This is an area-based planning estimate, not a cutting diagram. It does not optimize multiple squares, pieced fabric, rectangular remnants, directional prints, pattern matching, seam placement, or unusual construction methods. Actual yield can be lower when diagonal seams, trimming, inconsistent marking, fabric distortion, or the pattern's seam allowances use more material than the selected waste allowance.
Worked example
A quilt measuring 60 by 48 inches has a perimeter of 2 x 60 + 2 x 48 = 216 inches. Add 12 inches for joining and overlap, and the required binding length is 228 inches. With 10% waste, the planned cut-strip length is 228 x 1.10 = 250.8 inches.
For 2.5 inch strips, the unrounded square side is sqrt(250.8 x 2.5), or about 25.04 inches. Rounded up to the next half inch, the starting square is 25.5 inches. It fits across 42 inch usable fabric and represents 25.5 / 36, or about 0.71 yard of fabric length. A 20 inch scrap square makes 160 inches in theory; after 10% waste, its planned usable yield is about 145.45 inches, which is about 82.55 inches short of the 228 inch requirement.
Common questions
How do I calculate the perimeter for quilt binding?
For a rectangle, add all four sides: twice the length plus twice the width. Add any edges outside that rectangle, such as handles or curved sections, and include extra length for joining the final ends. The result is the binding length before a waste allowance.
What size square makes a given length of continuous bias binding?
Multiply the planned strip length by the full strip cut width, then take the square root of that area. Round the result upward to a practical cutting increment. The square must also fit across the usable width of the fabric to work as one unpieced square.
How wide should I cut double-fold bias binding?
The cut width depends on the finished binding width, fabric thickness, seam allowance, and the pattern's application method. Many quilt bindings use a 2.25 to 2.5 inch cut width, but a pattern's stated cut width should take priority. Enter the full width before folding, not the finished visible width.
Why is square area divided by strip width?
Area equals length multiplied by width. Rearranging that relationship gives length as area divided by width, so a square's area divided by the strip cut width gives the maximum theoretical strip length. Real continuous-bias construction loses some material to seams, marking, and trimming, which is why the calculator applies a waste allowance.
What if the required square is wider than my fabric?
You cannot cut that continuous-bias square as one unpieced piece across the stated usable width. Consider a smaller plan with pieced binding, multiple squares, a wider fabric, or a different construction method. This calculator flags the width shortage instead of presenting its purchase length as a usable one-square plan.
How much bias tape will my fabric scrap make?
For a square scrap, divide its area by the strip cut width for the theoretical length. Then reduce that result for the practical losses expected in your construction. A rectangular scrap can have the same area, but this calculator does not verify whether its shape can be converted into a continuous-bias loop.