Legal Question in Real Estate Law in California

It depends on how far off it is and why. "Rentable" square footage is often not the same as usable square footage. Structural members, utility voids and other spaces that cannot be occupied likewise can be included in the square footage. Ultimately the rent charged is for the space available. By using the overall square footage, it saves everyone the trouble of doing a bunch of geometry and math to determine the exact usable square footage, and then boosting the rent per foot by a few cents to get the same price for the space.

With that said, however, if the square footage is so far off as to have been materially misrepresented, then it may be grounds to void a lease or break it. I had a case in which the landlord had built a mezzanine inside warehouse space, increasing the square footage by 50%. They said the work was permitted, but when fire inspectors came through they said it was without permits and had to be torn out. The landlord tried to claim the lease was still valid, it they didn't even try to sue when my client stopped paying rent and moved to another property.