baby size??

Brittney
So I do hair and I have a few clients here and there say oh that's gonna be a big baby because I'm tall and my husband is tall... And they look at me like I'm huge but I look at myself and I'm just belly. I've gained 13 pounds and I'm 31 weeks.. We were both a little over 8 pounds. What do you usually go off of to figure out your baby's weight?