I am six weeks pregnant according to my ultrasound that was done today. when did i conceive?

Six weeks pregnant: Six week pregnant by ultrasound means you are roughly 4 weeks out from the conception date.

Conception: For a woman with a regular period, conception typically occurs about 11-21 days after the first day of the last period. Most women do not know the exact date of conception, and their conception date is merely an estimate based on the first day of their last period. An ultra sound is most accurate and using that and the above, can give you the most likely date of conception.