Adult Bulldogs tend to be much larger than other breeds of dogs, which means you would want to buy a bigger collar. A typical small-sized collar for a bulldog puppy should be around 15 inches long, and the medium-sized collar for medium dogs should be around 18 inches long.  For an adult Bulldog, it should be 20 inches or more long. Since bulldogs are not considered a toy breed, you wouldn't want to see any rips or tears, so a fabric-made collar with soft padding is better for their safety. The size of a collar will also depend on the dog's weight, so you can check the weight of your Bulldog and compare it with the measurements mentioned above.