3 dog years to human years by size
| Dog size | Human age | Life stage |
|---|---|---|
| Small (20 lb or less) | 28 | mature adult |
| Medium (21 to 50 lb) | 28 | mature adult |
| Large (51 to 100 lb) | 28 | mature adult |
| Giant (over 100 lb) | 31 | mature adult |
The old "multiply by seven" rule would say 21. The DNA-based formula from UC San Diego (16 × ln(3) + 31) gives 49. That formula was built on Labradors, so it fits medium and large dogs best.
What 3 looks like for a dog
Three is prime of life. Up to 80% of dogs show some dental disease by this age, so it’s a good time to start a tooth-brushing habit.
Frequently asked questions
How old is a 3 year old dog in human years?
Between 28 and 31 human years. Small dogs (under 20 lb) are about 28, medium dogs 28, large dogs 28 and giant breeds 31.
Is a 3 year old dog a senior?
For a small dog, no (mature adult). For a large dog it is not yet, and for a giant breed it is not yet.