Measure the crack the rain is coming through (4)

I believe the answer is:

acre

I'm a little stuck... Click here to teach me more about this clue!

'measure' is the definition.
(acre is a kind of measure)

I cannot understand how the rest of the clue works.

(Other definitions for acre that I've seen before include "Crusaders battlefield, now in Israel" , "Race (anag.)" , "amount of land" , "4840 sq yds" , "Imperial land measure" .)

I've seen this clue in the Evening Standard.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.