Different average values can be defined, depending on the statistical method applied. In practice, four averages are used, representing the weighted mean taken with the mole fraction, the weight fraction, and two other functions which can be related to measured quantities:
*Number average molar mass (), also loosely referred to as number average molecular weight (NAMW).
*Mass average molar mass (), where  stands for weight; also commonly referred to as weight average or weight average molecular weight (WAMW).
*Z-average molar mass (), where  stands for centrifugation ().
*Viscosity average molar mass ().
Here,  is the exponent in the Mark–Houwink equation that relates the intrinsic viscosity to molar mass.