聚合度（英语：Degree of polymerization，英文缩写为DP），为衡量聚合物分子大小的指标。以重复单元数为基准，即聚合物大分子链上所含重复单元数目的平均值，以DP表示。然而聚合物是由一组不同聚合度和不同结构的同系物之混合物所组成，因此聚合度是一个统计平均值，一般写成。

单体和平均聚合度的公式为，M_n是平均分子量，M₀是单体的分子量。

聚合度指聚合物分子链中连续出现的重复单元(或称链结)的次数。用n表示。例如尼龙66中结构单元是—OC(CH₂)₄CO—和—NH(CH₂)₆NH—，若用结构单元数表示聚合物的聚合度称为数均聚合度，用x表示。在聚氯乙烯中：x=n；在尼龙66中：x=2n。

The degree of polymerization, or DP, is usually defined as the number of monomeric units in a macromolecule or polymer or oligomer molecule.

For a homopolymer, there is only one type of monomeric unit and the number-average degree of polymerization is given by , where M_n is the number-average molecular weight and M₀ is the molecular weight of the monomer unit. For most industrial purposes, degrees of polymerization in the thousands or tens of thousands are desired. This number does not reflect the variation in molecule size of the polymer that typically occurs, it only represents the mean number of monomeric units.