Distance to measure right inside (5)
I believe the answer is:
metre
'distance' is the definition.
(unit of distance)
'measure right inside' is the wordplay.
'measure' becomes 'mete' (meting things out is measuring them out).
'right' becomes 'r' (common abbreviation).
'inside' indicates putting letters inside.
'mete' going around 'r' is 'METRE'.
'to' is the link.
(Other definitions for metre that I've seen before include "Poetic rhythm" , "Alignment of feet determines such" , "Moisture remover" , "Approximately 39 inches" , "Yard is smaller than this" .)