Fabric Shrinkage Calculator — Pre-Wash Allowance

Yes, pre-washing is strongly recommended for garments that will be washed. It removes sizing, preshrinks the fabric, and tests for colour fastness. The only exceptions are fabrics intended for dry cleaning only (like some wools and silks) or interfacing.

Standard quilting cotton shrinks about 3–5% in length and 1–2% in width. Cotton flannel can shrink 5% or more. Pre-washed or pre-shrunk cotton (labelled as such) will shrink much less, typically under 1%.

Most woven fabrics shrink more in the lengthwise (warp) direction than the crosswise (weft) direction. This calculator applies the shrinkage rate to length. For width, expect roughly half the lengthwise shrinkage rate.

Cut a 30cm × 30cm square, press it, then wash and dry it exactly as you plan to care for the finished garment. Measure again. The percentage change in each direction is your shrinkage rate. Use the custom option in this calculator to enter your tested rate.