Figure a measure to be a sure success (5)
I believe the answer is:
cinch
'a sure success' is the definition.
(I've seen this in another clue)
'figure a measure' is the wordplay.
'figure' becomes 'c' (I've seen this in other clues).
'a measure' becomes 'inch' (inch is a unit of length).
'c'+'inch'='CINCH'
'to be' is the link.
(Other definitions for cinch that I've seen before include "simple job" , "Doddle" , "piece of cake" , "Something easily done" , "A walk in the park" .)