I measure a 38 cm (according to DH anyway ), but the 38 cm ITM Elle bars that came on my bike were definitely too narrow for me. Whenever I got tired, my wrists would break to the outside when I rode on the hoods.

I switched to a 40 cm set of Ritchey BioMax Pro bars (not only wider, but a shallower drop and an ergo bend) and I really like them.

Actually, I've ridden 42s comfortably in the past. I can't ride on the tops of my 40s at all, but I could be comfortable there as well as on the hoods and the drops with the 42s. So it's possible that I don't actually measure 38.