Fabric shrinkage calculator
Dimensional change after washing in each direction, with growth reported as growth - not forced into a shrinkage number.
How this is calculated
For each direction, change % = (after − before) ÷ before × 100. For the area, use area change % = ((length after × width after) ÷ (length before × width before) − 1) × 100. The result is a percentage. It is not simply the sum of the length and width percentages.
Worked example. Benchmarks of 50 cm measure 48.5 cm lengthwise and 50.5 cm widthwise after washing. Length: (48.5 − 50) ÷ 50 = −3.00% (3% shrinkage). Width: (50.5 − 50) ÷ 50 = +1.00% (1% growth). Area: 48.5 × 50.5 ÷ 2,500 − 1 = −2.03%.
Quick table: cut measurement for a target finished dimension
Required pre-wash cut dimension (cm) using finished ÷ (1 − shrinkage) so that after washing the panel lands on the target finished measurement.
| Finished size | 2% shrinkage | 3% shrinkage | 5% shrinkage | 7% shrinkage | 10% shrinkage |
|---|---|---|---|---|---|
| 40 cm | 40.82 cm | 41.24 cm | 42.11 cm | 43.01 cm | 44.44 cm |
| 50 cm | 51.02 cm | 51.55 cm | 52.63 cm | 53.76 cm | 55.56 cm |
| 65 cm | 66.33 cm | 67.01 cm | 68.42 cm | 69.89 cm | 72.22 cm |
| 75 cm | 76.53 cm | 77.32 cm | 78.95 cm | 80.65 cm | 83.33 cm |
| 100 cm | 102.04 cm | 103.09 cm | 105.26 cm | 107.53 cm | 111.11 cm |
Questions
- How do I allow for 3% shrinkage in a pattern?
- If the finished dimension must be 100 cm after 3% shrinkage, divide 100 by 0.97. The cut dimension is about 103.09 cm. Adding 3% gives 103 cm, which shrinks to 99.91 cm. Apply the measured shrinkage for each direction separately, and do not add it again if the pattern already includes that allowance.
- Can I average length and width shrinkage?
- Keep them separate for pattern and fit checks. A fabric can shrink in length and grow in width, so an average can hide both changes. Area change describes the total surface area. It does not tell you whether a sleeve, body length or garment width will meet its finished measurement.
- Why are my results negative?
- Negative dimensional change is shrinkage; positive is growth. That is the sign convention of ISO 5077 and AATCC TM135, so the numbers can be compared directly with a lab report.
- Is growth a bad measurement?
- Not necessarily. Knits often grow in width while shrinking in length, and some finishes relax outward. It is reported as a real result.
- What benchmark distance should I mark?
- Test methods typically mark 350 mm or 500 mm (or 18 in) benchmarks on a larger specimen. Longer benchmarks reduce the relative error of your measurement.
- How do you calculate pattern allowance for fabric shrinkage?
- Divide the target finished measurement by (1 − shrinkage fraction) rather than simply adding the percentage. For a 70 cm finished length with 5% shrinkage, cut 70 ÷ 0.95 = 73.68 cm so that 5% shrinkage of 73.68 cm brings the garment back to 70.00 cm.
- Why should you average three benchmark pairs on each specimen?
- Fabric relaxation varies across the width and along the selvedge. Marking three parallel pairs in warp (or wale) and three in weft (or course) as required by ISO 3759 prevents a single distorted edge reading from skewing the pattern allowance.
- Can two fabric lots with the same average shrinkage share one wash pattern?
- Only if their range and behaviour during garment washing match. If one lot shrinks 2% and another 6%, averaging them to 4% leaves half the bulk order 2% oversized and half 2% undersized; shade-and-shrinkage grouping is needed instead.
Read the full guide
Sources & verification
Specimen marking and the dimensional-change formula follow ISO 3759 and ISO 5077; AATCC Test Method 135 uses the same definition for home laundering. The worked example is recomputed in the automated tests.