A simple cheap set of calipers would tell you for sure.
If you don’t have calipers (and don’t want to go spend $10-$20 at your local HF), it’s typically pretty easy to tell. .625 journals basically only come on LW or pencil profile barrels. Basically everything else (that isn’t a bull barrel or precision barrel) is going to be .750. Hell, you can usually just tell by looking at it.
As for looking it up, I’m not really sure. A picture would help.