If your on the app you can look at the week thing and it gives you a estimate of how much the baby should weigh
It says 2.2 pounds for 28 weeks so I'll say that's pretty average
My son was born early at 30 weeks and he was 3lbs 11oz. They gain a half a lb a week so that should be right.
Last time I checked I was 30 weeks and she was 4 pounds already.