FR4 measurement tolerances
If you look at the specifications from your supplier, you will see something like this: 


  STANDARD BOARD THICKNESS &amp; TOL.       From 0.10 mm (0.004") to 3.50 mm
  (0.138") Tolerance : IPC Class B


The "Class B" refers to the laminate thickness (no cladding), and you can refer to the IPC information for the relevant numbers

To get the overall tolerance for a multilayer board you have to add up all the tolerances of each layer and the copper thickness tolerances.