Complete Guide to Border Collie Size, Weight, and Growth Charts by Age

Border Collies are medium sized dogs, and like most herding breeds they have strong, athletic legs and thin bodies to maximize their agility, speed, and endurance.

A regular sized border collie is around 16-22 inches tall, with the males usually being slightly taller than the females. Border Collie Puppies grow quickly when they are under a year old and are fully grown by 18 months.

Over hundreds of years, collies have been selectively bred to maximize their herding abilities, resulting in a perfectly proportioned pooch for rounding up sheep.

In this article, we’ll look at Border Collie adults and puppies in depth, find out their size, weight, and growth charts at every age from puppy to full grown collie, so you know how big your border collie will be according to their age.

If you’re worried that your Border Collie might be too big or too small – check out my Obesity in Border Collies guide – where I explain how to make sure your collie maintains the perfect weight.

How big do Border Collies get?

Border Collies are medium sized dogs and can grow to a maximum size of around 22 inches (55cm) for males, and 20 inches (50cm) for females.

If you’re wondering how big that is, it’s roughly up to the knee of a 6 foot tall person.

While collies are generally roughly knee-high, they do have a tendency to jump up, and can reach well over 6ft when they want to.

If you think having a small 22 inches tall dog means they will curl up on your lap, or on the sofa – think again! When they are lying down, collies often stretch themselves out, taking up three times as much space as you thought possible.

How big do Male Border Collies get?

Male border collies can grow to a maximum size of around 22 inches (55cm), but their size varies according to several factors and a fully grown male border collie can be any size between 18-22 inches (45-55 cm).

Male border collies are usually larger than female border collies, although there are several factors that can influence their size, so this isn’t always the case.

How Big Do Female Border Collies get?

Female Border Collies are usually slightly smaller than males, although this isn’t always the case. Female Border Collies usually reach a maximum size of between 16-20 inches, or 40-50cm.

Female Border Collies usually have long, athletic legs and a thinner body than males, meaning they often weigh considerably less too.

Border Collie Size Classification

The American Kennel Club classifies dog breeds according to their weight.

According to the American Kennel Club Breed Weight TableBorder Collies usually weigh between 35 and 55lbs, or between 16 and 25 kilograms, which makes them a medium dog.

As you can see from the table below, this places most border collies firmly in the “medium dogs” weight classification, although occasionally at the bottom end of the “large dogs” weight classification.

Dog Breed Weight Classification Table:

ClassificationWeight (lbs)Weight (kgs)
ToyUp to 12 lbsUp to 5.4kg
Small12 lbs – 25 lbs5.4kg – 11.3kg
Medium25 lbs – 50 lbs11.3kg – 22.7kg
Large50 lbs – 100 lbs22.7kg – 45.4kg
GiantOver 100 lbsOver 45.4kg
Source: American Kennel Club

How heavy is a full grown border collie?

A fully grown border collie should weight between 35lbs and 55lbs, or roughly 16 to 25 kgs. Border collies should achieve their full grown weight by around 16-18 months old.

How heavy your border collie is depends on their diet, how much exercise they get, their build, whether they are male or female, what type of coat they have, their genetics, and even just what time of day it is.

Don’t worry too much if your collie’s weight fluctuates a bit month to month. As long as they get enough exercise and aren’t unhealthily overweight, a little bit of weight fluctuations is normal as the seasons change.

Luna’s favorite indoor exercise is chasing the vacuum around the living room…

Border Collie Puppy Weight Chart by age

Border Collie puppies grow quickly, maturing to full size at around 12 months old, although they are not fully developed until between 14 and 18 months.

Here’s a table showing how heavy a border collie puppy should be at each stage of their growth.

AgeWeight in pounds (lbs)Weight in kilograms (kg)
8 weeks4.0 – 8.0lbs1.8 – 3.6kg
9 weeks4.5 – 9.0lbs2.0 – 4.1kg
10 weeks5.0 – 10.0lbs2.3 – 4.5kg
11 weeks5.5 – 11.0lbs2.5 – 5.0kg
12 weeks6.0 – 12.0lbs2.7 – 5.4kg
13 weeks6.5 – 13.0lbs2.9 – 5.9kg
14 weeks7.0 -14.0lbs3.2 – 6.3kg
15 weeks7.5 – 15.0lbs3.4 – 6.8kg
16 weeks8.0 – 16.0lbs3.6 – 7.3kg
5 months11.0 – 22.0lbs5.0 – 10.0kg
6 months13.0 – 26.0lbs5.9 – 11.8kg
7 months15.0 – 30.0lbs6.8 – 13.6kg
8 months17.5 – 35.0lbs7.9 – 15.9kg
9 months19.5 – 39.0lbs8.8 – 17.7kg
10 months21.5 – 43.0lbs9.8 – 19.5kg
11 months24.0 – 48.0lbs10.9 – 21.8kg
12 months26.0 – 52.0lbs11.8 – 23.6kg
This table provides a rough estimate of the weight of a border collie puppy by age.

Border Collie Weight by Age

Border Collies grow quickly when they are puppies, especially when they are less than one year old.

After a year, Border Collies are usually at 95% of their final body weight, although they may still be developing up until 14-18 months of age.

How heavy should a full grown border collie be?

A fully grown border collie should weigh approximately 35-55lbs (11.3-22.7kg), however this van vary according to their gender, age, activity level, type of coat, diet, and genetics.

If your collie is happy and healthy and their body weight is in proportion with their size, there is nothing to worry about if they are a little it lighter or a little bit heavier than this rough estimate.

How heavy should a 3 month old Border Collie be?

A three month old Border Collie puppy should weigh approximately 6-12lbs, or 2.7-5.4kgs. Every puppy grows at a different rate, and if your pup is a little bit over or under this rough estimate it’s not a big deal.

How heavy should a 6 month old Border Collie be?

At six months old, a Border Collie puppy will be roughly 13-26lbs, or 5.9-11.8kgs. If your pup is a little under or over this rough estimate, it’s not a cause for concern. Just keep feeding them as much food as they need while they are growing.

How heavy should a 12 month old Border Collie be?

At 12 months old, your collie is almost fully grown and will weigh around 26 to 52 pounds, or between 11.8 and 23.6 kilograms. Collies generally finish growing between 14 and 18 months, so after this point there won’t be much additional weight to gain, but it’s important to continue feeding them a nutritious diet.

What age are border collies fully grown?

Border Collies grow rapidly until about 12 months old, after which point they will be at almost their full size.

Although border collies don’t grow much after 12 months, border collies are not fully grown until they are between 14 to 18 months old.

Female border collies mature quicker than males, becoming fully grown at around 14-16 months, and male border collies are fully grown at around 16-18 months.

What size should a border collie be at 3 months old?

At three months old, your border collie will be visibly still a puppy, with an oversized head and paws.

A three month old border collie will be approximately 16 inches high, and will weigh approximately 6-12lbs (2.7-5.4kgs).

What size should a border collie be at 6 months old?

At six months old, your Border Collie will be three quarters of their full size already, although they will still be less than half their adult weight, because they haven’t yet built up their full muscle mass and they still have some bone density to gain.

A six month old Border Collie will be approximately 18 Inches high, and will weigh approximately 13-26lbs (5.9-11.8kg)

When do Border Collies stop growing?

Border Collies stop growing taller at roughly 12 months old, although their bone density and muscle mass will continue to increase up until between 14-18 months.

Although you may not notice your puppy growing as quickly once they are over a year old, it’s important to continue giving them puppy food until they are 18 months old, so that they get all the nutrients they need to help their bones and muscles grow stronger.

What influences Border Collie Growth?

Collie growth is similar to other herding dogs, with the largest factor for predicting collie growth being genetics.

Collie growth is influenced by:

  • Genetics – Some collies are genetically predisposed to being larger or smaller.
  • Diet – A high quality puppy food will ensure your collie can grow to their full potential.
  • Exercise – Too much exercise is not good for young dogs, and can hamper their bone development.

About the author:

About the author:

Hollie and Border Collie

 Stuart MacPherson

Colliepedia Editor

 Stuart MacPherson

Colliepedia Editor

I'm an experienced collie owner from Scotland. I started Colliepedia to share everything I know about collies. All the pictures you see on colliepedia are of my beloved collie Luna

Learn More about me and Luna's story on the about page!