Yes, 23" = 7 3/8 (US, or 59/ 7 1/4 UK), my size, too. Edit: By the way, 'hard' hats like that (and, say, bowlers) are unforgiving in their fit. That can sometimes mean sizing up or possibly having it professionally fitted. It's not easy to find someone who can do that.
The price is high, but the apparent condition is good, the size is larger and they don't make 'em like that anymore.