According to Animal Planet, an adult male or female border collie typically weighs between 30 and 45 pounds. Males are taller, standing 20 to 23 inches, and females usually reach between 18 and 21 inches in height.
Though they only grow to be about medium size, border collies are very strong. Originally herding dogs, they are agile distance runners, able to change their speed and direction with ease. The breed tends to be very intelligent, alert, loyal and energetic, and they respond very quickly to training. When the dogs are not kept as herders, they are still driven to run after other animals. To prevent this, border collies require significant exercise and mental stimulation.