The surface-area-to-volume ratio has physical dimension inverse length (L) and is therefore expressed in units of inverse metre (m) or its prefixed unit multiples and submultiples.  As an example, a cube with sides of length 1 cm will have a surface area of 6 cm and a volume of 1 cm. The surface to volume ratio for this cube is thus
For a given shape, SA:V is inversely proportional to size.  A cube 2 cm on a side has a ratio of 3 cm, half that of a cube 1 cm on a side. Conversely, preserving SA:V as size increases requires changing to a less compact shape.