Fabric Shrinkage Calculator (Warp & Weft Wash Test)
Enter pre-wash and post-wash dimensions of test swatches to determine length (warp) and width (weft) shrinkage percentage.
Most costing and pattern mistakes with a new fabric trace back to one skipped step: nobody measured how much it shrinks in the wash. A fabric that loses 5 percent of its length will leave every garment 5 cm short on a 100 cm panel if the pattern is cut at finished size, and a booking that looked generous suddenly falls short. This guide explains how to read a wash-test result, turn it into a cutting allowance, and connect it to the Fabric Cost per Garment Calculator, where the shrinkage allowance shows up inside the consumption figure.
What is Fabric Shrinkage?
Fabric shrinkage is the change in a fabric's dimensions after washing and drying, measured separately along its length (the warp direction) and across its width (the weft direction). It happens because yarns relax, fibres swell and contract, and the tensions put into the fabric during weaving, knitting and finishing are released in the wash. Knitted fabrics usually shrink more than woven fabrics, and the two directions rarely shrink by the same amount.
Merchandisers and pattern makers measure shrinkage on a small test swatch before bulk cutting, because the bulk order must be cut larger than the finished garment and booked longer than the finished length. A test that shows 5 percent length shrinkage means every metre of raw fabric yields only 95 cm of washed fabric — and a booking made on finished length alone will fall short by that same percentage.
If the washed sample measures larger than the original, the result is negative: the fabric grew or stretched. Treat growth the same way, with the opposite sign — cut slightly smaller — and flag it to the supplier, because growth is often a sign of unstable finishing.
Formula
Shrinkage % = (Before wash - After wash) / Before wash x 100 Raw length for 100 m washed = 100 / (1 - Length shrinkage % / 100)
- Before wash: the original dimension of the test sample, in centimetres.
- After wash: the same dimension measured after washing and drying, in centimetres.
- Length shrinkage %: the warp-direction result. It alone drives the raw-length figure.
- Width shrinkage %: the weft-direction result. It drives pattern width allowances, not the raw-length figure.
- Raw length for 100 m: metres of unwashed fabric needed to end up with 100 m after washing.
How to Calculate
- Mark and measure a test sample before washing — length and width, at the same marked points, without stretching the fabric.
- Wash and dry the sample exactly the way the finished garment will be cared for, then let it lie flat and relax before measuring again.
- Measure the same two dimensions at the same points and enter all four numbers in the calculator.
- Read the length and width shrinkage percentages, plus the raw length needed for 100 m of washed fabric.
- Apply the percentages to the pattern: cut length = finished length / (1 - shrinkage / 100), and do the same for width using the width percentage.
- Book fabric on the raw figure, not the finished figure — and add cutting waste separately, because this tool does not include it.
Example
A cotton jersey for a 10,000-piece T-shirt order is wash-tested at 50 cm by 50 cm. After washing it measures 47.5 cm long and 48.5 cm wide. Length shrinkage is (50 - 47.5) / 50 x 100 = 5 percent, and width shrinkage is (50 - 48.5) / 50 x 100 = 3 percent. The calculator also shows that 105.26 m of raw fabric is needed for every 100 m of washed length, because 100 / (1 - 0.05) = 105.26.
Applied to the pattern, a finished body length of 70 cm must be cut at 70 / (1 - 0.05) = 73.68 cm, and a finished chest width of 50 cm at 50 / (1 - 0.03) = 51.55 cm. The check works backwards: 73.68 cm shrinking by 5 percent leaves 70.00 cm, and 51.55 cm shrinking by 3 percent leaves 50.00 cm. Booking on finished length alone would have left the order about 5 percent short of fabric — on a 10,000-piece order, that is a production stop, not a rounding error. For the money value of that fabric, see the Fabric Cost per Garment Calculator.
Assumptions
- The test sample represents the bulk fabric — same lot, same finish, same supplier.
- The wash and dry method matches the garment care label; a hotter or harsher wash will shrink more.
- Measurements are taken at the same points, without stretching, after the sample has relaxed flat.
- The raw-length figure covers length shrinkage only; cutting waste, end loss and inspection cuts must be added separately.
- One wash test may understate final shrinkage, since fabrics can shrink further over repeated washes. As good practice, repeat the test after several washes for repeat or long-life styles.