The inner cogs are approximately 1.6mm thick for both 10 and 11 speed road and MTB. The 11 speed spacers for the inners for both road and MTB are spec at 2.18mm thick. So the nominal 11 speed pitch is 3.78mm. However the outer 2 cogs with built in spacers are much thicker at the spacer, I don't remember how much, maybe 0.2-0.3mm.

My derailleur which is confusingly rated for both 10 and 11 speed mtb, moves a bit too far causing chain rub at the innermost or outermost cogs, so I swapped three of the 11 speed spacers for 10 speed spacers which are 2.35 mm. So I've increased my cassette width by around 0.5mm.

I also use a last position cog from a 10 speed cassette which is missing around 0.5 mm of the offset that an 11 speed last position cog has. (Which might partially explain the chain rubbing at the outer cogs if the derailleur is designed to move a greater distance at the outside)

With the entire cassette offset an extra 1mm outward, there's not enough thread engagement on the steel lock nut that comes with the cheaper Shimano cassettes. So I had to use the aluminum lock nuts that come with more expensive Shimano cassette because their threads are 1 mm longer.