The calculator can only compare the numbers you give it. Spend a little care on the sample, and your record becomes much more useful than a generic fabric shrinkage percentage.
1. Decide what you are comparing
Record the fabric description and the care process you will use. Follow the supplier’s instructions for that particular material. A result after one wash-and-dry cycle describes that cycle; it does not establish what will happen after every future wash.
Use a representative piece from the fabric you intend to cut. A swatch from an unrelated batch is not evidence for your cloth. If the intended care process is uncertain, resolve that before testing rather than choosing a hotter treatment to chase a number.
2. Keep length and width identifiable
For woven fabric, mark the lengthwise direction along the selvedge and the crosswise direction across the width. On other constructions, label two consistent directions so they cannot be confused later.
Mark measurement points inside the sample. Leave cloth beyond the marks so the measuring distance does not depend on fraying cut edges. Choose a size you can read accurately with your ruler. Pattern Scissors Cloth’s swatch-testing article is a practical further reading example of an oriented sample.
3. Write down the actual starting distances
Measure between the reference marks without stretching the cloth. Do not assume the marked square is exactly the size you intended to draw. If the actual starting length is 20.2 cm, record 20.2 cm. Keep all before-and-after measurements in one unit.
4. Repeat the measurement after care
Once your sample is fully dry and relaxed, measure between the same marks in both directions. Keep your ruler alignment and any pressing step consistent and record what you did. If the marks are missing or the sample is badly distorted, another sample is more useful than a confident-looking percentage.
5. Keep the observation with the result
Use the calculator, then print the record or download a CSV. On paper, add the fabric, wash/dry process, cycle count and date. Also note changes the calculator cannot see: skew, texture, colour, surface appearance or puckering.
Check the measurement before trusting a tiny difference
A 1 mm difference over a 20 cm reference distance is 0.5%. Over 10 cm, the same 1 mm is 1%. These are arithmetic comparisons, not an error estimate for your ruler. Very small changes can be difficult to distinguish from how you position or read the sample.
What a sample does not promise
A full length may behave differently, and additional cycles may produce further change. Dimensional change also does not describe colourfastness, garment fit or cutting-layout suitability. Cotton Incorporated’s CottonWorks guide provides technical background on why construction and processing matter.