Debate on sqft living space

[Stephen Homes]

I have a rental in NJ, and there is debate on what the actual sqft of the living space is. 

Where can I find the exact definitions of the living space area? 

I have a complete walk-in basement with closets, half a bathroom in the basement, and heat, but the rooms and sqft of it is not counted in the tax accessor papers (not even the half a bathroom).

Thank you