Ultrasound from lmp or ovulation?

T
Hey guys! I go in for my first ultrasound at 8 weeks. My husband freaked me out because he said the baby is only technically 6 weeks old from conception. When you calculate how far along you are and your first prenatal do you count the two weeks before ovulation it would I only be 6 weeks along? I want to make sure I can hear the heartbeat. 
Thanks!