A specimen is cut, a reference square is marked on the fabric, it is washed according to ISO 6330 (declared programme and temperature), dried under set conditions and measured again according to ISO 5077. The difference from the original size, in percent, shows shrinkage or growth in length and in width, reported separately for length and width.
The number of washes and the programme matter, so ask for the report, not just the value. Run your own test on every new lot before cutting, because small deviations multiply across a whole production run.
shrinkagedimensional-stabilityiso-5077
