It can be off by 3oz to 3 lbs and it's basically just luck if it's right or not. More times than not its off

Ultrasound right before I had my son estimated 7 lb 7 oz. He was 8lb 13 oz. so definitely a little off.

I was told my son was 5 lbs 4 oz and he came out 6 lb 4 oz

it's more so of an estimate but usually it's close to what they guess

@ash2014c, thanks.... I'm just wondering if anyone's has been right.

It's always a guess. Sometimes it's accurate, sometimes not.