I just went and measured the chain on my 11 speed Shimano 105. The chain is shimano slx CN-HG601. I was getting about 5.57 mm measuring externally from one side plate to the other going over the pin area.

Similarly I was getting about 5.85 mm on a Tiagra 10 speed equipped bike. All I know for certain is that is a Shimano HGX and I assume Trek put a 10 speed chain on their 10 speed bikes when it left the factory.

So that is a difference of .28 mm or .011 inch. Less than 3/64ths of an inch. To express it in fractions with less than a 10% error you have to go all the way down to 5/512.

Just FYI mostly.