Can you figure out conception date from six week sonogram? how accurate is it?

You can estimate: Conception date quite accurately. Properly performed and interpreted ultrasound examinations have a variability of 8% plus or minus the measured dating, so earlier is more accurate. Ultrasound dating at 6 weeks 0 days should have a 95% confidence range of 5 weeks 4 days to 6 weeks 3 days which is +/- 8%. Grab a calendar or online (search "ob wheel") to see estimated conception date.