I use 42cm marked bars which measure 41.x cm, something like 41.2 cm or so. I bought another same brand/model 40 cm, it measures virtually the same. Previously I had 43 cm bars outside to outside that measured about 41 cm c-c.

My shoulder width says to use 42s or even a 43. I've ridden 44s when I was doing long miles thinking I was a road racer (hahahaha…). I can't find it but there's a picture of me in here somewhere in a sprint in 2008 or 2009 and the comments went along the lines of "why do you have such a narrow bar?".