The demand for textile fibres is growing quickly. However, global cotton production has stabilized around 25 Mton/year. This is a sound development since cotton cultivation causes major sustainable development issues. Even if regenerated cellulose fibre production steadily grows, it is still only from a sixth to a fifth of cotton volumes. Hence, it is essential to find resource-efficient routes to generate alternatives to virgin cotton. There are many promising research initiatives that discover the possibility to utilize waste streams of neat cotton and cotton in fibre blends as raw materials for dissolving pulp for regeneration into, for example, viscose or Lyocell. However, there is a much simpler and energy-efficient route at hand. If fabrics are disintegrated mechanically, the separated fibres can be turned into yarn again. However, since fibre length is a key parameter to accomplish strong and durable textiles, fibre length loss upon tearing should be minimized. This study evaluates how fibre length distribution alters upon tearing of post-consumer cotton waste of two different constructions: denim and single jersey; and different degrees of wear, rendering four different fractions: (1) barely worn denim, (2) rather worn denim, (3) barely worn single-jersey and (4) rather worn single-jersey. Before tearing, the garments were dissembled, their yarns were characterized, fibre length distributions were manually determined for (1)–(4). Length analysis of the recovered fibres after tearing revealed that the length drop was most severe for (a) the finer single-jersey and (b) the barely worn fractions. The findings suggest that significant wear does not exclude from mechanical recycling.