Is it normal to overestimate square footage for a quote?

I'm in the process of collecting quotes to install granite on an outdoor kitchen.

I measured the surface and added the standard 1.5 inch overhangs and the calculation came up to about 32 sqft

But basically all quotes I've received so far are quoting me from 42 to over 50 sqft, which adds several hundreds more to the quote

Is there some extra measurement that I'm missing or are they trying to squeeze some extra money?

Here's my drawing with measurements, including overhangs, for reference

Thanks in advance!