Dogs age more quickly than humans, and, as many of us can attest, sadly don't stick around for the entire life of their owners. The "dog year" measure is an attempt to quantify this difference in lifespans to give an age to our furry pets as if they were to live as long as humans.

The most common system for calculating a pet's age in dog years is to multiply it by seven. The age of a 1-year-old Miniature Poodle in dog years would be 7 and that of a 2-year-old Great Dane would be 14. This system assumes an average lifespan of humans of 70 years and for dogs 10 years.

However, using this multiplier has several flaws, according to Stanley Coren, professor at the University of British Columbia who has written many books on dogs. For starters, 70 years is no longer the average lifespan of humans, and a dog's lifespan varies depending on its size and breed.

The fatal flaw, according to Coren, is that at 1 year old, dogs are able to reproduce puppies. This is not the case for a 7-year-old child.

Coren has come up with his own way to calculate a dog's age in human terms. In his system, a 1-year-old dog is like a 16-year-old person; at 2 the dog is like a 24-year-old person; and for the next three years until the dog reaches the age of 5, each year adds five human years.

Beyond age 5, the dog's size must be accounted for in the equation, Coren said. Typically, small dogs live longer than large ones. To account for this difference, Coren suggests adding four years of human life to the age of small dogs after age 5, and six years for large breeds.

Using Coren's system, a 1-year-old Miniature Poodle would be 16 dog years and the much larger, 2-year-old Great Dane would be 24 dog years. When each pup has graced the Earth for eight "real" years, the Miniature Poodle would be 51 dog years, and the Great Dane would be 54.