pregnant cats

I just posted that I have outside cats and one of them appears to be pregnant. Does anyone know how long the gestation period is?
I would like to get her contained in the barn so she won't take her kittens off to the woods. This is our first litter in a very long time!! I guess we waited too long to get her spayed. She is only 9 months old.
This will be her one and only, but it is exciting to be having babies!!

It is 63 days, give or take a day.

Thanks for answering, I do plan to have Jazzie spayed as soon as the kittens are born. And I will get the whole family their shots. Jazzie is a very small cat so I hope she only has a couple and I can keep them!