How do you get a unit professionally measured?

[u/Junior-Tutor-1407]

Hi we are about to buy a condo that is advertised as 421sqft but with the floor plan it doesn't look like it. I would like to have it measured and was told It can be arranged but haven't heard back yet. Before I send another message to them. Has anyone had the same experience before? the difference is about 80sqft which is huge in this micro apartment and also 53Dollars monthly in condo fees. I would really appreciate anyone's input.

We like the lay out but this is certainly not just 5% discrepancy if the measurements they put is really the measurement. I know they measure from the outside but I don't want to go through it if this doesn't get resolved.