Test the fabric you will use
Shrinkage depends on fiber, fabric construction, finish and washing/drying conditions. There is no one percentage for all quilting cotton or all flannel.
If a measured 60-inch piece shrinks by 3%, it becomes 58.2 inches: 60 × 0.97. This is an arithmetic example, not a promised shrinkage rate.
Before cutting
Follow the fabric maker’s care instructions and the pattern’s approach. Prewashing can change the usable width and purchased length, so measure again afterward. Small precuts may fray or lose their intended dimensions when washed; check their supplier’s advice.
Our fabric, backing and binding calculators do not automatically add shrinkage allowance. Enter dimensions measured after any preparation, and add extra purchase room when your project needs it.