There is no "simple" answer... not if I can help it.

The thickness of Metal Foil -Copper- depends on tolerance type: 10% for deposited and 5% for wrought.  The nominal thickness listed in IPC-MF-150 is .68 mils.  My opinion follows:
If I were producing copper foil daily, by the linear mile, it would be to my economic advantage to produce to the low side.  Hence the propensity is for the copper to come in the low side of tolerance.  After lamination (at laminate supplier and or PWB/PCB fabricator) the copper tendency is to reduce in thickness due to cleaning [cleaning aka etch, or if it is more palatable "micro etch"], it definitely doesn't get thicker.

It took me a while to adjust downward from .0007 to .0006 but I did, I feel it represents worse case.  Different treatments and tooth of copper also factors, but my simple answer is
half ounce tends to be .0006 inch thick in the deliverable PCB. Exact measuring will probably be .00061723.

Brad

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