Deductions & credits

I'd really like to see an answer to the important part of this question as I'm in the same boat.  If I co-own my home 50/50 as a joint tenancy with full survivorship rights, what do I enter as the total square footage of my home.  Do I enter 826 sq. ft which would be half of my homes total sq. ft. or would I enter all of the floor space: 1652 sq. ft.  I've been told both ways - which is correct?