I have a white female dog, we got her from the dog pound and they told me that it was a boxer mix, but other people tell me she's an american bulldog, how can I find out? she looks more like an american bulldog.

A vet can usually tell you which features from what breed is in your dog. You can never be 100 percent certain but they are usually very good at seeing what breed it is.

The kennel club have a site with Dog standardsTry this linkhttp://www.thekennelclub.org.uk/item/435