A chart tracking human years to dog years is available at WebMD. The chart includes the age of the dog and the equivalent human age for small, medium and large breeds.
The idea that one dog year equals seven human years is overly simplified, because this can vary based on size, breed and developmental stage. Dogs mature more quickly than human children. Also, smaller dogs usually live longer than larger dogs, but they also mature quicker in their first few years. A small dog is 20 pounds or less, a medium dog is 21 to 50 pounds, and a large dog is more than 50 pounds