It�s the same for all dogs, regardless of breed; about 9 weeks.
How will you know? A vet can tell you by feeling how the dog�s uterus is changing. If you don�t ask a vet, until the puppies are born you won�t know for sure although there will be changes in her behaviour which will give you clues. For eg, increased nesting (scrabbling in bed and soft furnishings), shorter time between need to wee, might look a bit hot and bothered sometimes (panting, shallow breaths). And nearer her due date she�ll have a fuller tummy and teats.
Hope this helps.