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Quick answer
Dog sizes are sorted by weight, and the usual cut-offs run: teacup under 4 pounds, toy 5 to 12, small 2 to 22, medium 24 to 57, large 59 to 99, giant 100 and up. No two sources fully agree on where one bracket ends and the next begins. The gaps are a few pounds and rarely enough to move a dog into a different category, so use the ranges your vet or your insurer uses.
There is no single official line between a small dog and a medium one. The American Kennel Club publishes height, weight and life expectancy for each breed, not a size class, so every size chart you find online is somebody’s own grouping.
This guide does the same, and says so. We sorted 18 breeds into four groups by the weight on their AKC breed page. The groups are ours and approximate: a Dalmatian at up to 70 pounds and a Boxer from 65 could sit on either side of the medium and large line. The figures in the tables are the AKC’s, and where the page gives separate numbers for males and females we show the male figure.
Why Size Matters
The AKC article on size and lifespan reports that, within a species, a small body size is associated with longer life and slower aging, and that the dog is a species with a huge size range. It also says body size was the most important variable in predicting lifespan in the University of Washington study, more important than whether the dog was purebred.
Size also changes what you buy. Our guides to dog beds for small spaces and orthopedic beds for large and senior dogs start from the dog’s weight.
Small dogs
| Breed | Height | Weight | Life expectancy |
|---|---|---|---|
| Boston Terrier | 10-12 in | 12-25 lb | 11-13 yr |
| Pomeranian | 6-7 in | 3-7 lb | 12-16 yr |
| Beagle | 13 in and under | under 20 lb (13 in and under) | 10-15 yr |
| Chihuahua | 5-8 in | not exceeding 6 lb | 14-16 yr |
In the studies the AKC summarizes, small dogs had the longest median lifespan, 14.95 years in a University of Washington analysis of 169,000 dogs. Weight still matters inside this group: in a study of 12 breeds, overweight Yorkshire Terriers lived 13.7 years against 16.2 for those at a normal weight.
Medium dogs
| Breed | Height | Weight | Life expectancy |
|---|---|---|---|
| Border Collie | 19-22 in (male) | 30-55 lb | 12-15 yr |
| Basset Hound | up to 15 in | 40-65 lb | 12-13 yr |
| Bulldog | 14-15 in | 50 lb (male) | 8-10 yr |
| Australian Shepherd | 20-23 in (male) | 50-65 lb (male) | 12-15 yr |
| Dalmatian | 19-24 in | 45-70 lb | 11-13 yr |
The same analysis puts medium dogs at a median of 13.86 years. The breed pages show how much one label hides: the Bulldog is listed at 8 to 10 years, the Border Collie at 12 to 15.
Large dogs
| Breed | Height | Weight | Life expectancy |
|---|---|---|---|
| Boxer | 23-25 in (male) | 65-80 lb (male) | 10-12 yr |
| Golden Retriever | 23-24 in (male) | 65-75 lb (male) | 10-12 yr |
| German Shepherd | 24-26 in (male) | 65-90 lb (male) | 12-14 yr |
| Rottweiler | 24-27 in (male) | 95-135 lb (male) | 9-10 yr |
Large dogs came in at a median of 13.38 years in that analysis. The AKC also reports that in a study of 74 breeds and more than 56,000 dogs, large breeds died more often from cancer than small ones, and the lead researcher said large dogs age at an accelerated pace.
Giant dogs
| Breed | Height | Weight | Life expectancy |
|---|---|---|---|
| Great Dane | 30-32 in (male) | 140-175 lb (male) | 7-10 yr |
| Saint Bernard | 28-30 in (male) | 140-180 lb (male) | 8-10 yr |
| Newfoundland | 28 in (average male) | 130-150 lb (male) | 9-10 yr |
| Mastiff | 30 in and up (male) | 160-230 lb (male) | 6-10 yr |
| Irish Wolfhound | 32 in minimum (male) | 120 lb (male) | 6-8 yr |
The breed pages give the shortest ranges here, 6 to 10 years. The AKC article shows that breed still matters inside a size group: among giants, Great Pyrenees lived 11.55 years against 9.63 for Great Danes.
How to Use This
Use the tables as a starting point and read the full AKC page for any breed you are considering. Two dogs of the same breed can differ in size, and a lifespan range is an average, not a promise.
Related: why small dogs bark so much and German Shepherd pros and cons.
Sources
- AKC article on size and lifespan (University of Washington, Göttingen and WALTHAM Centre studies it summarizes)
- American Kennel Club breed pages: Boston Terrier, Pomeranian, Beagle, Chihuahua, Border Collie, Basset Hound, Bulldog, Australian Shepherd, Dalmatian, Boxer, Golden Retriever, German Shepherd, Rottweiler, Great Dane, Saint Bernard, Newfoundland, Mastiff, Irish Wolfhound
Frequently asked questions
What counts as a small, medium or large dog?
Small is usually under 22 lbs, medium 22 to 55 lbs, and large 55 lbs and up. Breed standard and frame matter as much as the number on the scale.
How do I know how big my puppy will get?
Paw size is a rough hint. A better estimate is the breed average, or for mixes, doubling their weight at about 16 weeks.
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