The microscopic scale (from Greek: μικρός, mikrós, "small" and σκοπέω, skopéō "look") is the scale of objects and events smaller than those that can easily be seen by the naked eye, requiring a lens or microscope to see them clearly. In physics, the microscopic scale is sometimes regarded as the scale between the macroscopic scale and the quantum scale. Microscopic units and measurements are used to classify and describe very small objects. One common microscopic length scale unit is the micrometre (also called a micron) (symbol: μm), which is one millionth of a metre.
By convention, the microscopic scale also includes classes of objects that are most commonly too small to see but of which some members are large enough to be observed with the eye. Such groups include the Cladocera, planktonic green algae of which Volvox is readily observable, and the protozoa of which stentor can be easily seen without aid. The submicroscopic scale similarly includes objects that are too small to see with an optical microscope.
In thermodynamics and statistical mechanics, the microscopic scale is the scale at which we do not measure or directly observe the precise state of a thermodynamic system – such detailed states of a system are called microstates. We instead measure thermodynamic variables at a macroscopic scale, i.e. the macrostate.
We shall call a system 'microscopic' (i.e., 'small scale') if it is roughly of atomic dimensions or smaller (say of the order of 10 Å or less).