# Bias binding calculator

Binding is cut two ways, and the arithmetic differs. Straight-grain strips run across the roll, so the count is the length needed divided by the usable width, and the fabric bought is that many strip widths. Continuous bias seams a square into a tube and cuts round it, producing one unbroken strip: a square of side S yields about S² divided by the strip width, so the square needed is the square root of the length times the width. Only bias will go round a curve.

Source: https://fabricmeasure.com/calculators/bias-binding-calculator/
Last updated: 2026-08-20 (method v1)
Published by FabricMeasure.

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## The formula

```
strip length = length to bind + extra for corners and joins
strip width  = finished width x fold factor

STRAIGHT GRAIN:
  strips = ceil(strip length / (fabric width - 2 x join allowance))
  fabric = strips x strip width

CONTINUOUS BIAS (a square seamed into a tube and cut round):
  square side = sqrt(strip length x strip width)
  fabric = one square of that side
```

The bias formula is an area identity, not a convention: a square of side S yields
about S^2 / W of strip, so S = sqrt(L x W).

The rule that "bias costs 41% more" describes cutting strips FLAT from a rectangle,
where the triangular corners are wasted. The continuous-tube method is what avoids
that loss. Which method uses less cloth depends on the run: straight grain wins on
short runs, bias wins on long ones. Both are always costed.

ONLY BIAS WILL GO ROUND A CURVE. Woven cloth stretches on the 45-degree diagonal and
almost nowhere else.

## Fold factors

| Construction | Cut at |
| --- | --- |
| Double fold (binds an edge) | 4x finished width |
| Single fold (turned once) | 2x finished width |
| Cut width entered directly | 1x finished width |

## Defaults

- Extra for corners and joins: 30 cm
- Lost at each strip end (straight grain): 1.5 cm
- Cut increment: Nearest 10 cm

## Worked example

400 cm of 1.2 cm double-fold binding from 112 cm cloth.

| Step | Working | Result |
| --- | --- | --- |
| Strip width to cut | 1.2 cm finished × 4 for a double fold (binds an edge) | 4.8 cm |
| Strip length needed | 400 cm to bind + 30 cm for joins and corners | 430 cm |
| Strips across the roll | 430 cm ÷ 109 cm usable per strip | 4 strips |
| Fabric off the roll | 4 × 4.8 cm strip width | 19.2 cm |

Straight grain: 19.2 cm off the roll.
Continuous bias: a 45.4 cm square.

## Common questions

### How big a square do I need for continuous bias binding?

The square root of the strip length times the strip width. For 5 metres of binding cut at 5 cm, that is √(500 × 5) = 50 cm square. The method conserves area almost exactly, which is the whole reason it exists — cutting bias strips flat from a rectangle wastes the triangular corners at each end.

### How wide should I cut binding strips?

Four times the finished width for a double fold that encloses an edge, twice for a single fold turned once. So a 1.2 cm finished double-fold binding is cut at 4.8 cm. These are the constructions rather than conventions: the cloth has to go round the edge and back on itself.

### Is bias binding really more expensive than straight grain?

It depends what you are counting, and the calculator shows both. Measured in metres off the roll — what you pay for — straight grain wins throughout, because a strip runs the full roll width while a bias square uses only its own side. Measured in cloth consumed, the square wins, which is what matters when you are cutting from a piece you already own. The old 41-per-cent rule describes cutting bias strips flat, which is exactly what the continuous-tube method avoids.

### When do I have to use bias rather than straight grain?

Whenever the edge curves. Woven cloth stretches on the 45° diagonal and almost nowhere else, so a bias strip goes round a neckline, an armhole, a curved hem or a round cushion and lies flat. A straight-grain strip on the same curve ripples on the outside and pulls on the inside.

### My bias square is wider than my fabric. What now?

Cut two smaller squares and make two strips, joining them once. Two squares of about seven-tenths the side give the same total area, and one extra join is a small price. Alternatively cut on the straight grain if every edge you are binding is straight — there is no advantage to bias on a square corner.

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