How do I allow for shrinkage in a T-shirt pattern?

Short answer: Measure the finished fabric's shrinkage in length and width after a defined wash and dry, then enlarge the pattern in each direction by enough that the washed garment reaches the specification. Because shrinkage is a percentage of the final size, the allowance is calculated as final length divided by (1 minus shrinkage), not simply final plus shrinkage. For 5% length shrinkage, a 70 cm body needs a pattern of about 73.7 cm. Apply length and width separately, use shrinkage from the actual bulk fabric lot, and confirm by washing sample garments. Pattern allowance works only if fabric shrinkage is consistent; if it varies widely between lots, fix the fabric finishing first.

Measuring fabric shrinkage

• Use ISO 3759 for preparing, marking and measuring specimens.
• Wash and dry following a stated ISO 6330 procedure, the one closest to customer care.
• Calculate dimensional change with ISO 5077.
• Test each bulk lot, not only the development fabric.

Calculating the allowance

• Pattern size = finished size / (1 – shrinkage as a decimal).
• Example: 52 cm chest with 2% width shrinkage gives about 53.1 cm.
• Apply length and width separately; they are rarely the same.
• Ribs, tapes and trims may shrink differently and need their own allowance.

Confirming on garments

Make a set of garments with the adjusted pattern, wash them following the care label, and measure against the specification. Check fit points such as body length, chest, sleeve length and neck opening, not only overall size.

A worked example

For the shirts in the question, the team measures 5% length and 2% width shrinkage on the bulk lot. They lengthen the body pattern by about 5.3% and widen it by about 2%, wash three samples, and find body length within 1 cm of the specification. The neck rib, which shrinks less, is left unchanged.

Common mistakes

• Adding the shrinkage percentage instead of dividing by one minus shrinkage, which leaves garments slightly short.
• Using development fabric figures for a bulk lot that was finished differently.
• Applying the body allowance to ribs and tapes that shrink less.
• Testing only one wash, when some fabrics keep shrinking over the first few washes.

Limits

Customers wash and dry in many ways, so garments may still change in use. Tumble drying usually causes more shrinkage than line drying. Allowances depend on consistent fabric.

Facts, recommendations and uncertainty

Established: pattern allowance compensates for measured fabric shrinkage when calculated by direction from test results. Recommendation: test each lot and confirm on washed samples. Uncertain: real customer washing, which may differ from the test procedure.

Sources and further reading

• ISO 5077:2007 — Determination of dimensional change in washing and drying
• ISO 6330:2021 — Domestic washing and drying procedures for textile testing
• ISO 3759:2011 — Preparation, marking and measuring of fabric specimens and garments for dimensional change

Standards and regulations are referenced by their published scope. Test parameters, cycles and pass levels should be agreed with your laboratory for the specific product; legal requirements should be confirmed for each destination market.