A practical guide

Start with the actual project

Measure the project perimeter and add joins and tails first, then calculate fabric from the full required strip length.

Write down each measurement with its unit. Enter lengths in the displayed unit and keep counts separate from dimensions. If a product specification provides a value, use that value for the exact material or equipment involved.

Work through the calculation

1. Open the calculator and replace every example input that differs from your project.
2. Read the named results and their units. A negative remaining-space result describes a fit problem, not a usable dimension.
3. Save a baseline before changing assumptions. Adjust one measurement at a time to see what drives the result.
4. Use the comparison table and the exact values beneath the chart to check the effect of a change.
5. Export a worksheet or print the final result, then verify a sample before making an irreversible cut or purchase.

Project-specific checks

1. Enter cut width, before folds. Finished binding width is a different measurement.
2. Area equivalence is an estimate; joins, diagonal layout and edge losses affect practical yield.
3. A square gives an approximate continuous-bias starting size; round upward for cutting.
4. Check whether your project uses single-fold, double-fold or quilt binding before choosing width.

Read rounding correctly

Whole-item counts may round upward to cover a requirement or downward to fit a space. The formula reference identifies ceil and floor operations. Displayed decimals are rounded for readability; calculations keep the underlying numeric precision.

When a number looks wrong

First check units and inside-versus-outside dimensions. Next check whether allowances were included twice. Finally compare the input assumptions with the project-specific checks above. The worked scenarios provide a reproducible starting point.