How far along will doctor say I am when I go?

I’m confused about the whole weeks thing. So do they only go off of your last period (07/12/2019)? Do they add in how long your cycle is (34days) or what day you think you ovulated (08/01/2019)?

Or do they just measure the baby an tell you how far you are?

I feel silly for not knowing but I’m curious and need some help. Thank you!