Italian to English Law/Patents Real Estate

Taken from an atto di compravendita.
I understand that "are" translates as "ares", although I think it would be better to convert into square metres...
My main query is the "ca." - if it stands for "circa" it doesn't make any sense, so I presume it is another unit of measurement - if so, which one?
I've been looking everywhere but can't seem to track it down.
Many many thanks in advance.