The permittivity of free space (a vacuum) is a physical constant equal to approximately 8.85 x 10-12 farad per meter (F/m). It is symbolized o. In general, permittivity is symbolized and is a constant of proportionality that exists between electric displacement and electric field intensity in a given medium. In many materials, particularly glass and certain plastics, is substantially greater than o.
If o represents the permittivity of free space (that is, 8.85 x 10-12 F/m) and s represents the permittivity of a particular substance (also specified in farads per meter), then the relative permittivity, also called the dielectric constant r, of that particular substance is given by:
r = s / o
= s x 1.13 x 1011
Also see Table of Physical Units and Constants.