First Ultrasound- measuring further along

Tayler

Hey ladies, I went in for my first ultrasound and I thought I was 6 weeks 5 days. However, Due the ultrasound tech said I’m measuring 7 weeks and 2 days which means I’d really be 8 weeks on Sunday. Do I do by the first day of my last period or what I’m measuring based off of the ultrasound? 🤔