Body Mass Index (BMI) Calculator

Body Mass Index Calculations

This tool can be used to calculate body mass index, or BMI, which is a measure of a person’s mass, or weight, relative to their height. The calculator only requires three inputs by the user:

  • Selecting U.S. Customary or Metric units from a drop down list
  • The user’s height, stated in either centimeters or feet and inches
  • The user’s weight, stated in either kilograms or pounds

The calculator then provides the user with two pieces of information:

  • The calculated BMI value
  • The category into which the calculated BMI value falls, as indicated by the BMI value’s background color

Healthy Weight Guidelines

Calculating BMI is extremely simple and requires only two inputs to determine its value. Simplicity is what makes BMI so useful and why so many health care organizations use it to categorize a person’s weight. And while some organizations, and publications, make it sound like BMI is a way to definitively categorize a person’s health, the accompanying table should be viewed as a “rule of thumb” only.

Weight CategoryBMI Value
UnderweightLess than 18.5
Normal (healthy weight)18.5 to 25
Overweight25 to 30
ObeseOver 30

History of the Measure and its Limitations

While BMI was first proposed by the mathematician Adolphe Quetelet back in the mid 1800s, it rose to prominence in the 1970s when several doctors observed the impact of the Western diet on society and the increase in a number of chronic diseases associated with overweight individuals. However, even the dietary experts that promoted its use understood its limitations too. For example, the BMI categories many NOT be appropriate for:

  • Individuals age 20 and younger
  • Lean athletes with high muscle to fat ratios
  • Bodybuilders
  • Older individuals that may have lost height

BMI categories are also based on statistics gathered from predominantly white populations. For this reason, they are considered less accurate for other races.

Risks Associated with High BMI Values

BMI can be an effective screening tool, and it can help identify the risk of developing conditions such as heart disease or diabetes. Since the categories were developed statistically, insurance companies often use this data to determine the likelihood someone will reach an advanced age and the premiums paid on health and life insurance policies. In addition to being used as a screening tool for cardiovascular disease and diabetes, BMI is also used to identify people with an increased risk of developing arthritis, liver disease, some cancers (breast, colon, and prostate), high blood pressure, and sleep apnea.

If you want to learn more on this topic, take a look at our blog article Using BMI to Measure Health Risks.