The Mark–Houwink equation, also known as the Mark–Houwink–Sakurada equation or the Kuhn–Mark–Houwink–Sakurada equation or the Landau–Kuhn–Mark–Houwink–Sakurada equation or the Mark-Chrystian equation gives a relation between intrinsic viscosity  and molecular weight :
From this equation the molecular weight of a polymer can be determined from data on the intrinsic viscosity and vice versa.
The values of the Mark–Houwink parameters,  and , depend on the particular polymer-solvent system. For solvents, a value of  is indicative of a theta solvent. A value of  is typical for good solvents. For most flexible polymers, . For semi-flexible polymers, . For polymers with an absolute rigid rod, such as Tobacco mosaic virus, .
It is named after Herman F. Mark and Roelof Houwink.