The ratio of the mean-square end-to-end distance,

, of a
linear polymer chain in a theta state to

, where

is the number of rigid sections in the main chain, each of length

; if all of the rigid sections are not of equal length, the mean-square value of

is used, i.e.
In simple single-strand chains, the bonds are taken as the rigid sections. The recommended
symbol is:
(
when

).
Source: