Are you the proud owner of a Border Collie puppy and wonder what his final size will be? Simply enter his current weight and age into our puppy growth calculator, and we will predict his adult weight and growth chart.

Border Collie Weight Calculator & Growth Chart

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How big will my Border Collie get?

Like many herding dogs, Border Collies are a medium-sized breed. The American Kennel Club gives the following sizes for adult Border Collies:

• Females are 18-21 inches tall and weight 30-45 pounds
• Males are 19-22 inches tall and weigh 35-55 pounds

Because this breed was once “purpose bred”, there is a large variation in size. 

Border Collies originate in the UK, where they were once used to tirelessly herd huge flocks of sheep. When breeding dogs, farmers did not pay much attention to looks such as color or size. They were pairing dogs with the best working abilities. This created extremely intelligent, high-drive dogs with a range of physical appearance.

Some Border Collies might be tiny - even as light as just 25 pounds for some very small females - or they can be rather large. 

Especially large and heavy-boned dogs are usually seen in show lines (bred for conformation showing) rather than working lines.

How big is a 3 month old Border Collie?

At 3 months old, a Border Collie puppy weighs around 12-15 pounds. As all dog breeds, Border Collies grow rapidly in the first half year of their life. After this time, their growth tapers off.

It is interesting to note that the weight and size at birth is not a good predictor of the final size of a dog. Birth weight is largely determined by the intrauterine placement of the puppy (that means where in the uterus he was lying, and how well his placenta provided nutrition). Some puppies are born the smallest of the litter, and then quickly catch up and overtake their larger littermates in growth.

Until a puppy is about 12 weeks old, his size and growth curve is not correlated with his final adult weight. Only once a pup reaches the 3 months mark, we can make accurate predictions about his future size.

How big is a 6 month old Border Collie?

As a medium-sized dog, a 6 month old Border Collie starts to already slow down his growth. You can expect him to weigh around 20-25 pounds at this age. Your dog will look less like a puppy, and more like an adult dog. If he is a rough-coated Border Collie, his hair is getting longer and his body is becoming tall and thin.

Don’t confuse this rapid physical growth with his mental development though: At 6 months old, a dog is still very much a puppy and requires intense interaction, socialization and training - daily!

What is a good weight for a Border Collie?

Your dog’s ideal weight will always depend on his size. What is a good weight for a tall Border Collie would make a smaller one overweight (e.g. a 21 inch tall dog would be at a healthy weight when weighing 42 pounds - but an 18 inch tall dog would be way too heavy!).

Rather than measuring weight by a number, you should always assess the dog’s overall body condition. Run your hands along his sides. Can you feel the ribs without having to press in? If yes, he is in great shape.

If you have to dig in your fingers in order to feel his ribs, he needs to lose a few pounds. Should the ribs stick out, feed him a bit more!

When is my Border Collie fully grown?

Border Collies are mostly full-grown around the age of 12 months. After this, they might continue to gain a few pounds and build more muscles, but you should not expect your dog’s size to change considerably after his first birthday.

If you own an intact male, your dog’s chest will become broader and deeper as he ages. If he has a rough coat (meaning long fur), this fur will also continue growing.

In neutered males and females, these changes are less apparent.

Some very small Border Collies might already be done growing at 10 months of age. Sometimes, this is due to the fact that they were actually mixed with a smaller breed.

Why is my Border Collie so small?

Some Border Collies stay very small. As described above, this breed was never developed to fit a certain physical breed standard. Border Collies were bred to work hard, make smart decisions, and get the job done! How big exactly they were was secondary to their work ethic and ability.

Some lines produce especially small and light-boned dogs. They have in the last decade also become very popular in certain dog sports, such as flyball, agility and disc dog. Your Border Collie is probably completely healthy and simply a small specimen of the breed.

Of course, you should always check with your veterinarian if your dog’s small size goes along with:

• Vomiting or diarrhea
• Lethargy and none of the typical “bounce off the walls” Border Collie energy
• Changes in coat - such as a lot of hair loss, bald patches or a coat that feels rough
• Changes in eating and drinking habits

If you notice any of the above symptoms, it might be that your dog’s small size is caused by a medical issue - in this case, have him checked out asap!

Border Collie mixes

Not all Border Collies that are sold as pure-breds actually are pure-bred dogs. Unfortunately, a lot of irresponsible and money-hungry breeders produce mixed breeds and sell them for a high price. This happens in the Border Collie world as well.

If your breeder did not give you papers on the puppy you purchased and your puppy grows slowly but appears healthy, chances are that you did not actually purchase a full-blooded Border Collie. Your dog might be mixed with a smaller breed (that looks similar to Border Collies - such as a Papillon). Of course, in that case he will not grow up to reach the size of a pure-bred Border Collie.

But this will not matter - he will be an amazing companion in any case!