58 to 63 days from first breeding
All dogs are 9 weeks or around 63 days.
Average length is 59 to 63 days though can be a little sooner(like 57) or later (no more than 70). You're vet can probably advise you of a more accurate due date when you go in for your ultrasound or x-ray. Start taking temperature around day 57 and when it drops to 98 (or 99) your dog is in first stage labor and the pups will arrive within 24 hours or there's a problem and you need to call your vet.