2 things:
1) There are various well defined standards for measuring square footage. Do you count mechanical/ service areas or not? Measure to the centerline of a wall, face of finish, or outside? Gross, net, rentable, etc. all get defined differently by different organizing bodies (BOMA, FICM, etc). For multi-unit apartment buildings the standard is ANSI/BOMA Z65.42010, which largely updates and clarifies the older NAHB standard.
2) The above generally doesn't matter when it comes to renting apartments. Partly because almost no one gets it right (by any standard much less the one they should be using), and partly because either way you're going to have to go look at it and decide if it's enough space for you and your stuff. No measurement standard I know of gives any weight to how efficiently space is laid out.
Just use the published SF to find places in the right ballpark and then go check it out.
Good advice but my current apt is 750sq ft and I think I need at least this much space honestly. If this one calculates to less than that its going to be very tight. And again, I applied for it (free application luckily) sight unseen as they do not have one available to view.
Not sure what I'll do if my app is approved. Require a viewing before signing any leasing documents?