Sort out right measurement for trousers? (5)
I believe the answer is:
girth
'measurement for trousers?' is the definition.
'sort out right' is the wordplay.
'sort out' indicates an anagram.
'right' is an anagram of 'GIRTH'.
(Other definitions for girth that I've seen before include "Some tack" , "Target of diet" , "Size of waist perhaps" , "Circumpherence" , "Body's circumference around the middle" .)