(plural dog years)
- (informal) A period of time in the life of dogs, defined such that the average life expectancy of a dog in "dog years" is numerically equivalent to the average life expectancy of a human. A 4- and a 5-year-old dog are about as mature as a human of 28 to 30 years and 33 to 35 years, respectively.
- A unit of age relative to the species being considered, defined such that an animal's age in "dog years" is the equivalent age of a dog in calendar years.
The two definitions complement the two definitions of "human year" respectively. By the first set of definitions, a 6-year-old dog would be described as having an age of 6 human years or 40–50 dog years. By the second set of definitions, the same dog's age would be given as 6 dog years or 40–50 human years.