cm2s

cm2s, written as cm2/s in publications, is the unit centimeter-squared per second. It is a derived unit used to express diffusivity and other area-per-time coefficients on a centimeter scale. In SI units, the corresponding unit is square meters per second (m^2/s); the conversion is 1 cm^2/s = 1×10^-4 m^2/s, and 1 m^2/s = 10^4 cm^2/s.

In practice, cm^2/s is commonly used in chemistry, physics, and materials science when measurements are naturally expressed in centimeters, such as diffusion of solutes in liquids at laboratory scales, diffusion of gases in air under standard conditions, or movement within porous media at small scales.

Typical diffusivity values vary widely: for small molecules in water, D ≈ 1×10^-5 cm^2/s; for gases in air, D can be ~0.1–0.3 cm^2/s; in solids or layered materials, effective diffusivities may be much smaller or larger depending on structure.

Because cm^2/s expresses area per unit time, it describes how quickly an area is effectively explored by a diffusing species rather than a simple rate. It is often encountered in a diffusivity D, tortuosity, or permeability context, where D relates to mean squared displacement over time: <r^2> ≈ 6Dt in three dimensions.

Note: cm^2/s is a unit of diffusivity; it should not be interpreted as a flow rate. Other quantities, such as flux, require additional factors like concentration gradients and area.