I adopted a "lab mix" from the pound today. She is approximately 5 months old and weighs 36 lbs. How big do you think she will get?

Bigger dogs generally grow for the first 1 - 1 1/2 years of their life.

It depends on the mix, genetics, exercise and diet.

There's no way to tell, you'll just have to wait and see.

I have a lab mix. The father was a border collie, weighed under 40 pounds. The mother was a lab mix, weighed under 60 pounds. My dog weighs 80 pounds.

It really depends on a lot of different things.

I would say, just based on her size at 5 months, that she'll probably be around 60 pounds full grown.

That's just a guess though.

Congrats on your new family member. :)

Another post where I had to spread the rep Alty :)
I'll still add my two cents worth though haha

When breeding dogs there is a lot to consider about genetics.
The mother and father have 2 sets of genes each (one dominant and one recessive)

Every characteristic of the dog, from coat color and height to health issues to temprament and passed down by these genes.

With a mixed breed dog it is near impossible to tell what they will look like as you don't know what genes will be passed on.

For example if you have a lab x border collie like Alty does, when they were bred the owners would have had no idea what the puppies would have looked like. Some may have inherited the border collie coat, other the lab coat. Some will inherited to borders size, others won't.

Also, just to really confuse you the grandparents of the dogs also have an effect. Alty's dog is 80 pounds so it is more than likely that the labs mother or father was a larger dog and that was passed down to the dog via a recessive gene. This mean that it basically sat dormont in the lab until it was passed down to Altys dog.

Makes your head spin huh?

Congrats on your new addition, sounds like a nice combination, would love some pictures.