10 weeks??

Hailey

I've been meaning to ask this cause it's something idk about but I doubt anyone else does either... It says I'm 10 weeks today. That's 10 weeks from the first day of my last period. Would my baby really measure up to be a 10 week baby? Is this really how everyone accurately counts the weeks of their pregnancy? Full term is 40 weeks. Is that 40 weeks counting from the day of your last period? I'm confused 🤔😳