Bigger beer about right! (6)
I believe the answer is:
larger
'bigger' is the definition.
('large' can be a synonym of 'big')
'beer about right' is the wordplay.
'beer' becomes 'lager' (lager is a kind of beer).
'about' indicates putting letters inside.
'right' becomes 'r' (common abbreviation).
'lager' placed around 'r' is 'LARGER'.
(Other definitions for larger that I've seen before include "Bigger, greater" , "bigger,greater" , "more stout" , "Comparatively bigger" , "More bulky" .)