This is never an easy question as there is no exact science to it, this much vets and other recognised canine authorities can agree on!

credit https://www.thedoggurus.com/wp-content/uploads/2016/03/shutterstock_113624929-646x600.jpg

How do we try and work it out for you?

For us, as we rarely find the mum with pups, and have only ever once had the mum and dad as well as their litter, we can’t even say the breed for sure, so we always go on what the vet whose care they are under says, and regularly update weights and ages to show their rate of growth. We also use a handy puppy growth chart that can help you have a good guide as to what size they will be as an adult.

But we’ve had different vets venture different opinions as to breed mix and sizes, and the younger they are, the less likely the breed or weight estimate will be accurate, unless we rescue them on their day of birth and have the mum, and at least some knowledge about the dad.

So of course the older the puppy is, and the more we know about their parents, the more likely the vet will be able to estimate breed and adult size.

The breed

We are asked what breed a pup is a LOT. Simple answer we almost never know. And as almost all rescue dogs are mixed breed, it’s even harder to work out possible size (or breed for that matter.)

Possible ways to work out adult weight/size

Most authorities on pup size agree that any pups tend to be between the size of their mum and dad,with the boys more likely to be close to the dad’s size, and girls perhaps closer to the mum’s size. But we, like many other rescues, almost never get to even see the dad. And this is not a hard and fast rule, we’ve had tiny boys become the biggest adult, girls outgrow the boys; and, especially with dogs on the street or those who’ve ended up in a kill shelter, sometimes there can be more than one dad, and we’re sure we don’t need to draw you a picture of why that might be…
Some estimate pup adult sizes by looking at their weight at a certain age, like at 6 weeks for small breeds (multiply that weight by 2, then by 2 again). and at 14 weeks for medium to large breeds, double that weight and add on half their 14 week weight.
Others use this ‘universal formula’:To do this you must divide your weight in kg by age in weeks and then multiply that number by 52. That is, If for example your dog weighs 5.5 kg and is 12 weeks old, divide 5.5 by 12 to get 0.45 and then multiply it by 52 (how many weeks are in a year) which is 26-27 kg (medium). We recommend a calculator for this one!
Small breed dogs tend to reach their adult size younger than larger breed dogs too. Small breeds stop growing at 10 months and by 12 months, they reach their full adult size. Medium breeds may reach their adult size between 12 and 16 months and large and giant breeds, reach their full size between 18 months and 2 years old.

But for any of these calculations to be effective you'd need to have some starting points such as date of birth and a 'guess' in mind of their adult size, so regular weighing also needs to be done.

You could also check paw size in relation to the rest of them, the bigger they are in proportion, the more likely you’ll have a big adult dog.
But some think paw size is not reliable at all and suggest checking how long a pup is stretched out, and this could indicate a possible adult height. Not sure how that works with Dachshund , JRT or Corgi mixes, all long body but short legged dogs, to name but a few! Or at the other end- greyhounds, Salukis, or wolfhounds with very long legs…
Even vets and other official 'dog bodies' look for things like dominant or 'breed typical’ colours to ‘guess’ a possible breed mix and therefore a possible size, despite the fact that there are only two basic pigments that determine the colour of dogs: eumelanin (black) and phaeomelanin (red). These colours split off into hundreds of different combinations and patterns, even in the same litter, as well as being dependent entirely on the breed mix. Black fur can dominate round the nose in a hundred different breed mixes as well and we are a black dog rescue for the most part. We are talking of tens of thousands of genes, all combinations of the mum dad and their ancestors so colour is not an indication of breed by itself, though many ‘greeders’ think it is. This is why you find even ‘pure breeds’ dumped to die by people breeding dogs if they come out the ‘wrong colour’. For example, while the ‘gene' for black is dominant; the one for yellow is recessive (can easily be ’taken over’ by another colour). If a dog has at least one copy of the dominant black ‘gene', it will be black. For a dog to be yellow, like a Labrador for example, a colour produced by the recessive 'gene', it must have two copies. A black dog might produce yellow puppies if it carries a recessive 'gene', but a yellow dog cannot produce black puppies unless bred to a black. To think of a dog of having, say, ‘Collie colours' or 'Lab colours', as both breeds are known to be a in certain size range (medium), looking at colour can help. However, it’s not always that simple. Just look at this photo of just some variations of Collies and Labs here. Dogs are unique as a species for their massive variations of size and/or breeds (you don’t get the same variations with domesticated cats, for example)

And this is just Border Collies! You also have Shelties, rough coated, smooth coated, Shetland... Credit https://www.animalwised.com/all-border-collie-colors-patterns-combinations-3505.html#:~:text=%20All%20the%20color%20types%20of%20the%20Border,merle%2C%20a%20genotype%20is%20given%20in...%20More%20

And there is more than type and colour of lab- US, UK and Canadian variants, and the colours can be yellow, tan, black or chocolate. Credit https://www.animalwised.com/the-different-types-of-labrador-retrievers-3543.html

You may want to get a DNA test to try and see if there are any unexpected large or small breeds hiding in the mix. Many of our adopters have done these and have had some amazing and sometimes unexpected results. And you’d never tell by 'looking' at the pup, even as the pups' regular vet. Do note even DNA test manufacturers state they do not guarantee accuracy and some even refund if you get ‘megamutt’ (too mixed to know for sure).

Credit https://www.rearfront.com/wp-content/uploads/2018/02/Massive-Dog-Breeds-2.jpg

Our vets regularly weigh the dogs at the estimated age intervals as above so we can see the increases and try to be as accurate as we can in the size. But there can be a smaller or bigger dog back in their ancestry, which can affect these estimates, and other issues like

too-early neuter can affect growth (the dog can end up bigger than expected if neutered too young, e.g. if done before proper testicle descent/ under 6 months old) and
growth spurts caused by having top quality food in their new forever home. This is even more likely when raw fed (we are a raw feed rescue- do see our blog about our feeding recommendations and why we recommend raw feeding whenever possible).

But what if we get pups with just a mum, or no mum at all, and the pups are already born?

Well we have even less clues, as without having an exact date of birth we can’t even do any of the above calculations to the day, again it’s vet’s best educated guess as to age.

credit https://c8.alamy.com/comp/D2EDR2/dog-cavalier-king-charles-spaniel-adult-and-four-puppies-black-and-D2EDR2.jpg

So unless you’re getting a pedigree dog (certificated, with full provable bloodline) or an adult dog, you simply will never know for sure what size a rescue dog will be as an adult (or what breed mix a rescue dog is) just by looking and even regular weight checks and thorough examinations by veterinary experts. We do our best to inform, and only use vet’s weights and professional breed estimates, but these are not infallible.

Therefore there is no applicable ‘Trades Descriptions Act’ that apply to rescue mixed breed dogs, such or indeed any description is always given in the name of transparency as a guide only and from expert veterinarian opinion only. That only applies if a 'greeder' has ripped you off with a ‘pure bred’ dog either with no pedigree certificate or a forged one. Here a simple DNA test of the pups and their sire and dam (mum and dad) will find the court would side with the buyer, NOT the seller, in cases like that.

But we don’t ’sell’ dogs- we are a rescue and adopters only pay a dog’s bus fare, VAT, UK legal costs (chip, ID tag etc) and the like, not for the dog itself like a breeder, and adopts under our terms and conditions. If rescue mixed breed dogs could be so judged legally, which genetics and the law says they can’t, then the RSPCA would be bankrupt as they’ve called every puppy that crosses their threshold (if not tiny) collie crosses, and if small, JRT mixes, for example, for the past thirty years at least, to our knowledge alone! When they do this, they are not 'lying’- they are saying to potential adopters ‘this dog is likely to be medium sized’ or ‘this dog is likely to be smaller sized’. Even then, litters get mixed up- one of our team had a Dog’s Trust dog 20 years ago described as a JRT mix, and as part of a litter of JRT mix pups, as a pup from 9 weeks old (ish) but she was longer haired and a different colour- and she ended up being 22kg and looking more like a huge Yorkie! No vet could ever say her breed mix for sure but one thing they did know is that she was NOT a JRT mix of any sort!

Plus when you register a dog’s chip with Petlog- as we do for all our dogs- (run by the Kennel Club) and a breed mix is defined by a vet or other authority or official body, it means the Kennel Club takes our word for breed mix, and can permit your dog to compete officially as that breed mix in such things as agility (an agility team needs one declared breed or breed mix per team to be able to compete, and in some agility competitions, and some breed mixes are excluded due to their known superiority at agility skills in some solo competitions) and other fun and stimulating activities for your dog.

And proper non breed events exist like Scruffts, which also has rules in the opposite way- any ‘recognised’ breed mixes can’t take part but while a DNA test is not required a dog may be be excluded for 'looking’ too much like a certain breed; even from a ‘recognised’ silhouette.

credit http://1.bp.blogspot.com/-9I5Az9-1wdM/URJPInEictI/AAAAAAAACqg/gwcmrFwymsg/s1600/dogs-breeds.jpg

And why are the rules so vague? Because there’s no way of telling for sure the breed of a dog without watching the mum and dad mate, knowing the full bloodline of those dogs, then keeping the mum away from all dogs once she has conceived and being there at the birth.

Thus the only way to know for sure what size your dog will be is to get them when they are 2 years old or more, or as said above in the case of breeding dogs with known lineage of both mum and dad if getting a puppy.

So applicants looking for small dogs because they

have a landlord contractual requirement for a certain size of dog***
due to age of the potential adopter (over 21s only)
or physical health restrictions that would prevent appropriate care of a bigger dog

we will always advise you get an adult (also taking into account character/temperament/lifestyle of the dog; experience, lifestyle and temperament of the adopter; and more, to ensure the best match). The last thing we want is a dog returned to us because it’s ‘the wrong size’ for legal or contractual reasons, and therefore we would blacklist anyone

who demanded a puppy with a size limit not due to the reasons above, ignored our advice, then decided it’s too big (would you return a kid if it grew too big!?)
who surrendered that dog for aesthetic or personal preference reasons alone.

We would also stop or review an application or at the least be very wary of an applicant who insisted on having a small dog because

'the kids are scared of big ones' or
that only small dogs are cute,
or they think they will bark less or be easier to train.

This is not the case!

Only certain known smaller breeds are seen by professionals as being easier to train, or less noisy. In fact smaller dogs tend to bark more than bigger ones, and be more vocal in general. So applicants with an unrealistic view of a puppy or small dog will be advised accordingly by our team, as this may not be the match for you no matter how much you want a 'cute, small and fluffy' puppy. Puppies grow!

***And this is one reason we do ask for written landlord permission should someone renting apply for a dog, and we need to know there and then if there is a size restriction for a dog on that property. Should an adopter not disclose any requirements like this and it becomes an issue later on, this would also lead to being blacklisted and RBU enacted (For more on our RBU or Rescue Back Up, please see our blog on the subject).

For more reading:

https://www.vetbabble.com/dogs/getting-started-dogs/how-big-will-puppy-get/ goes into more details and also includes a weight calculator but be advised, to-the-day birth dates are rare in rescue dogs.

Go here for the science (genetics)! https://vcahospitals.com/know-your-pet/genetics-basics-coat-color-genetics-in-dogs

For more on how to compete in agility events, and the rules in general on how and where to get involved https://www.crufts.org.uk/dog-exhibitors/agility/qualification-for-crufts/

First compiled August 2019, edited January 2021.

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