This question makes a lot of unnecessary and more harming non related assumptions. Most notably the exclusion of its grammage as base value, as that is the way paper handling is done.
For all practical purpose Tofro's answer already covers a good estimation as a bit less than 0.1 mm.
Paper thickness is related in a linear fashion to its weight. All it needs to go from the ubiquitous notation of grammage (weight per surface size) to thickness is to include its specific weight (weight per volume). Dividing these will easily deliver thickness. 4th grade math assumed.
With grammage in g/m^3 and specific weight in g/cm^3 this gets transformed into a simple
grammage * specific weight / 1000
The specific weight of a certain paper is defined by its style and how 'smooth' (*1) it is. For most practical purpose it ranges from 0.6 to 1.3 ) g/cm^3. As a result 80g/m^2 paper may range at 0.048 to 0.104 mm
Now, having done the basic math, there is also a less theoretical way. People like to have simple numbers, so paper maker also came up with a simple definition system for thickness of standard papers, defining a standard 'Volume' specifier which gets given out by paper makers to further define their paper.
It got set (*2) to 1 for a paper of a specific weight of 1 g/cm^3. Sounds superfluous, but using the term Volume as unit less classification instead of a specific weight with a complex unit seems to improve usage by non-nerds (*3).
For practical purposes, a volume 1 paper has a thickness in mm at exactly its grammage divided by 1000. So a volume 1 paper with 80 g/m^2 will have a thickness of 0.08 mm. Similarly, a 100 g/m^2 paper will have a thickness of 0.1 mm. Paper of different thickness is noted with a different 'Volume' like 1.5 for a thicker one, which with the same 80 g/m^2 will measure 0.12 mm. (80*1.5/1000)
This is especially great, as average office paper is of 'Volume' 1 type.
Bottom line: Just take the grammage, divide it by 1000 and apply the 'Volume' specifier. If none is given then 1 is a good value to start with for fine office paper, while cheaper and/or simple recycles one goes up to 1.2-1.4 (*4).
(Classic) Printer use, they are made to work well with paper of 0.2 mm or more (0.17 being a punch card type paper) and more importantly, several layers of such. Usually the transport mechanics (straight vs. bend over some rollers) and the stiffness was more important than thickness itself. Mainframe chain printers could work well with forms with fanfold 'paper' of 8 (!) layers paper and 7 intermediate carbon layers (*4) - although, one had to be rather exact when positioning the paper box and quite careful mounting the paper.
*1 - The German term paper makers use here is 'Gestrichen'. I have heard the term 'coated' in similar situations in English. Thicker papers are often called double or triple gestrichen/coated. Keep in mind, I'm definitely no expert about paper making, especially not in multiple languages.
*2 - Yes, as with everything there's a DIN fixing it, just don't ask me about the number.
*3 - It's also a real great example why the metric system is so easy. If everything is noted down using the same unit system, conversion usually breaks down to simple shifts - in this case shift right by 3.
*4 - Yes, that felt more like a diaper than printing paper:)