If you can get a finger in you're about 1cm, BUT the inner about outer parts of the cervix can dilate at different rates, so if you can put a finger in and feel the membranes then you're a 1, if you can get your finger in but not feel bubs you might still be closed inside.

Effacement plays a big part in dilating for that reason, the thinner the cervix gets the more the inner and outer openings match up, kwim? It's hard to judge effacement unless you touched your cervix a lot before, but you can guesstimate by how much fingertip is inside the cervix when you've inserted it as far as it'll go. The whole fingertip to the first knuckle would be about 2cm, so you'd be about 50% effaced, the bottom of the fingernail would be about 1cm, so you'd be about 75% effaced.

I was 1-2cm dilated and 50% effaced at 40 weeks and went to 41+4! I'm sending the good vibes your way, but if you PLAN to be 14days overdue, you can only be happily surprised

Bx