How incorrect of a due date can an ultrasound show?

I believe that my due date from my ultrasounds were 2weeks wrong. They say i were due March 9th, but i believe i were due Feb 22nd. I ended up having my bub on March 7th and she looked well cooked. I would say they could be wrong but probably no more then 2 weeks either way of the date they give you. You have 2 rememeber the date is only an estimate, if you know what day your last period was or when you last had sex, if your able to work out your own date i would say somewhere in between your date and the ultrasound would be the due date.