The standard is 1" for 8' & 9' tables 1 3/4" on the Empress Line and all 12' tables.
Most new slates just meet WPBA standards of + .020" length & +.010" width. At Custom Billiards we hand hone all Empress table slate to + .005" or better. With a hand honed slate you not only get a flatness that meets WPBA standards, you get one that exceeds it, giving you decades of worry free & accurate play.