A healthy body mass index for men is in between 18.5 and 24.9, with anything either side of that range being underweight or overweight. The body mass index is calculated from a person's height and weight and can be found using a table from WebMD or a calculator at NHLBI.NIH.gov.
The body mass index system does not account for muscle or fat composition of the body, making it potentially inaccurate to assess the health of an individual. According to Men's Health, the system was actually invented to measure the population on a broader scale, rather than just one person. Despite its intended use, the calculation method took off in popularity for individuals as well. A checkup by a doctor offers a better evaluation of a person's health.