The well-liked delusion is that a dog gets 7 years old each year; others think it's even 10. But the thing is canine aging is quicker during the first 2 years of its life. After the first 2 years the ratio settles down to 5 to 1 for small and medium breeds. For large breeds the rate is 6 to 1, and for giant breeds the rate is 7 to 1.
Example, at 10 years of age a Great Dane would be 80 years old while a pug would only be 64. (Please refer to the Chart)
But what if you've taken a dog whose age is unknown? Well, Vets have other ways to estimate dog's age like checking on their teeth, muscle tone, eyes and coat. You can read more about it at Dogster.com