Plastic limit (PL) is the moisture content at which a fine-grained soil cannot be remolded without cracking. The plastic limit test requires repeated rolling of a soil sample into a thread until it reaches a point where it crumbles.

Plastic limit (PL) along with shrinkage limit (SL) and liquid limit (LL) comprise the Atterberg limits.

The PL is expressed as a percentage of the weight of the oven-dry soil, at the boundary of plastic and semi-solid consistency. It is the moisture content at which the rolled soil will begin to crumble when rolled into a thread 3mm or 1/8^th inch in diameter.