Beer on right is bigger (6)
I believe the answer is:
larger
'bigger' is the definition.
('large' can be a synonym of 'big')
'beer on right' is the wordplay.
'beer' becomes 'lager' (type of beer).
'on' means one lot of letters goes inside another (as in clothing 'on' a person).
'right' becomes 'r' (abbreviation).
'lager' going around 'r' is 'LARGER'.
'is' acts as a link.
(Other definitions for larger that I've seen before include "Bigger, greater" , "Comparatively big" , "More bulky" , "Greater in size" , "More comprehensive" .)