I'm not sure you can tell this in millimeters?
Its more like 160g/m2 (german weight) what I often found here in the forum is 110lb (us weight) but I don't know what it is in chinese format sorry
You may not realise it yet, but weight per area (or per ream of 500/1000 sheets, if you're in the US or Japan) is exactly what you're talking about, because that's what paper strength is measured in. Nobody will sell you a pack of "0.1742 mm paper".
But to answer your question: I'm using 250 g/m² and one sheet is about half a millimetre thick. Check my WIP thread, post #1, for a picture. There seems to be a jump in thickness around 200 g/m² though, because anything below that is hardly thicker than normal office paper.