The speed that a dog can run would be determined by the breed. A greyhound can run 30 to 40 miles per hour but have been clocked as high as 45. Toy breeds can run 5 to 10 miles per hours but only for short distances.
1 Additional Answer
On average dogs run at about twenty miles per hour. The fastest dogs are greyhounds and they run at some forty miles per hour. Dogs run pretty fast.