Which floor is ชั้นหนึ่ง?

In most Thai buildings ชั้นหนึ่ง, floor 1, is the floor you walk in on, the way Americans count. Malls often add a G (ground) and an M (mezzanine) button, which shifts every number above them, and car parks go down to B1 and B2. Some condos skip floor 13 or 4, or call it 12A, because those numbers feel unlucky to many buyers. When someone tells you อยู่ชั้นสาม "it's on the third floor", count the way the lift buttons do, and in a mall check the floor directory near the escalators, which lists every shop by floor.