one of our years is said to be 7 dog years. So a dog which has lived for 10 years would be 70 dog years. It is an approximation due to the ways dogs age but varies according to breed and other factors. So if someone is 30 years old and you are 20 years old you would be 140 years old in dog years.

A dog year is a unit of measurement equal to one seventh of a year, or approximately 52 days. It is primarily used to approximate the equivalent age of dogs and other animals with similar life spans. It is based upon a popular myth regarding the aging of dogs that states that a dog ages seven years in the time it takes a human to age one year. Here "dog years' might refer to the fact that the speaker is younger, but the amount is only countable when it is expressed in 'dog years". In other words, the amount is less than a normal year.

A dog year is a mythical unit of time based on the theory that a dog matures seven times faster than a human so a 15-year-old dog is supposed to be the equivalent of a 105-year-old person. The figurative meaning is that one will feel that much more time passes than what actually passes because the time will pass very slowly.