I don’t know that there is a standard hank. It was apparently an idea for industry but not one strictly adhered to.
I took a quick survey of some hanks that I have on hand or have used recently. Most are worsted weight and 100gr. Of course, the yardage varies a bit but is around 200-220 yds.
This undoubtedly also varies with yarn weight. I see fingering at 200g per hank and 700-900 yds.
So, that said you could weigh the hanks and taking the size yarn (ww, fingering, DK) into account make a guess at yardage. Not so helpful but easier than opening the hanks.