In physics and mechanics, mass distribution is the spatial distribution of mass within a solid body. In principle, it is also relevant for gases or liquids, but on Earth their mass distribution is almost homogeneous.

In astronomy, mass distribution has a decisive influence on the development of, for example, nebulae, stars and planets. The mass distribution of a solid defines its center of gravity and influences its dynamic behavior, for example, oscillations and final rotation.

A mass distribution can be modeled as a measurement. This allows for point masses, line masses, surface masses, as well as masses given by a volume density function. Alternatively, the latter can be generalized to a distribution. For example, a point mass is represented by a delta function defined in three-dimensional space. A surface mass on a surface given by the equation f (x, y, z) = 0 can be represented by a density distribution g (x, y, z) δ (f (x, y, z)), where is the mass per unit area.

Mathematical modeling can be done by potential theory, by numerical methods (for example, a large number of mass points), or by theoretical equilibrium figures.

In geology, aspects of rock density are involved.

Rotating solids are considerably affected by mass distribution, whether they are homogeneous or inhomogeneous; see torque, moment of inertia, wobble, unbalance and stability.