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Weight Based Dog Age Calculator

Calculate a dog's age in human years by using the dog's age and weight.
Weight: lbs
Age: years
Human Age: years
Human Age (7x): years
It's the age-old question, how old is my dog in human years? Many factors contribute to answering this question. A dog's breed, health, nutrition, and weight are certainly contributing factors.

This dog age calculator determines a dog’s age by factoring in the weight of the dog. Small dogs typically live longer lives than heavy dogs making the standard ('human age' = 'dog age' x 7) equation inaccurate.

This dog age calculation is based on a chart developed by Fred L. Metzger, DVM. William Fortney, DVM, R.T. Goldston, DVM and Ernest Ward Jr., DVM adapted the chart. Griscotti’s was able to develop an equation that would closely resemble the original chart. Some assumptions were made, the original data contained weight ranges. The mean of these ranges was used as the actual weight reflecting the dog's human age. For example, the chart indicates that a 10-year-old dog that weighs between 21 and 50 pounds is approximately 56 in human years. In order to form an equation, an exact weight had to be extracted. The mean was used as the exact weight, yielding that a dog weighing 35 pounds is approximately 56 years old in human years. This conversion was performed for each listed weight range below 91 pounds. The ranges described in the chart are the following: <20lbs small dogs, 21-50lbs medium dogs, 51-90lbs large dogs. Dogs greater than 90 lbs are considered to be giant dogs. The calculated equation is optimized for weights below 90 lbs, though it can be used on weights above 90 lbs. No specific weight could be extracted from the chart for dogs weighing more than 90 lbs, so accuracy above 90 lbs is unknown.

The equation developed is parabolic in nature for determining the dogs age increment per year. The equation matches the reported human age found in the chart by +/- 1.16 percent at all weights up to 90 pounds. A best-fit analysis was performed to find an equation that given a weight and dog age, the result will closely match the reported chart data. The equation is used on dogs’ ages 3 and up. For dogs under 3 years old, the equation is used to calculate the human age of a 3 year old dog at the given dog weight. A parabola is projected though this point (human age) giving a focal length. The focal length is used with the given dog age to find a corresponding human age. Again, this is done at dog age 3 and under only. The rational behind using a parabolic equation is that it provides a nice age curve showing that dogs mature rather quickly in the early years, then once mature, the amount of human years per dog years is constant.

The equations used are approximations of dog age. They seem to be better than the 7x equation. Give the calculator a try! We would love to improve the equation, send us any data or insight on the subject. (

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