Allotted amount (6)
I believe the answer is:
ration
'allotted amount' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for ration that I've seen before include "Limit to a fixed amount, be sparing" , "Limit quantity as of food during scarcity" , "Dole out portion due to shortage" , "Restrict the consumption of something" , "Parcel out scarce food, say" .)