It depends on too many things.
Something to think about though - dogs are pack animals, and they are easily scared. So long as they aren't foaming at the mouth, or trained otherwise (such as a police dog, I'm not talking about your average family pet) all you have to do is show them you aren't afraid of them, and that you are in charge. You don't necessarily have to beat them, just let them know that they don't want to attack you, and they will back off.
The vast majority of dogs that I have ever encountered, upon meeting me, are either scared of me or indifferent. The first time I met Thorne's dogs, they just kind of looked at me and sniffed me a bit, then forgot about me. He told me how they tend to snap at people they don't know, didn't do it to me. It's all about how you react to them. I'm used to dogs, know how to act around them, and they could tell.
Another example is my mom's dog. Half yellow lab half golden retriever. It's a big dog, could probably fuck me up pretty good, and its scared shitless of the world. I can't even get it to come up to me the first 15 minutes I'm at my mom's house.
Cliff's: A dog TRAINED to fight, I wouldn't want to fuck with. A family pet, or even a wild dog (without rabies), I wouldn't have any worries.