Body Mass Index (BMI) Calculator
BMI stands for "Body Mass Index," a ratio between weight and height. It is a mathematical formula that correlates with body fat.
GRAPH of the Percent increase in risk by level of obesity.
Definition of Healthy Weight1
Maintenance of a healthy weight is still a major goal but is now secondary to weight maintenance at any level. Use of a cutoff Body Mass Index (BMI) to establish the upper bound of a healthy weight is based on the use of a definition of obesity that is related to pathologic sequelae rather than an arbitrary definition. The cutoff point used to define obesity will depend on whether the cutoff point is based on morbidity or mortality. For example, several recent studies designed to address this problem have demonstrated that mortality increases significantly above a BMI of 25 (5-7). However, the prevalence of diabetes begins to increase well below a BMI of 25 (8,9). Because the most significant and reliable consequence of a disease is mortality and because the designation of obesity at a point below a BMI of 25 will label well over half of the population obese, the committeesuggests that use of a BMI of 25 to define the upper boundary of healthy weight appears the most reasonable definition. Use of this cut point is consistent with the cut point recommended by the American Institute of Nutrition Consensus Conference (10). Because body fat cannot be readily measured, weight appears to be the most appropriate surrogate.
Inclusion of a graphic that shows a graded risk for weights for height above a BMI of 25 has substantial merit, insofar as a graded risk is consistent with the dose effect of a rising BMI and helps move the perception of weight from an either-or discussion. The principal difficulty with a graded risk approach is the determination of where to draw the lines. The use of colors to indicate that the risks are not clear-cut is a format preferable to the use of lines. A relative risk of two for death and diabetes occurs between a BMI of 25 and 33 (range 26.9-32.9)(references 5-9). Although arbitrary, these data would suggest that a risk-related gradient should utilize a BMI of 25 to 28 or 29. Use of shading reflects the lack of a clear-cut point or consensus on where the line should be drawn and emphasizes that risk varies with the severity of the disease.
The area below the healthiest weight represents a BMI of less than 19 (15th percentile). This area is not named because it is not clear whether a weight below this BMI is unhealthy. Further data are necessary to demonstrate the point at which the risks associated with a low BMI increase. The revised guideline states that there may be risks associated with a low BMI, particularly if involuntary weight loss has occurred.
To calculate body mass index for a given height and weight, use the formula below.
w BMI = --- h2
Where w is weight in kilograms (pounds divided by 2.2), and h is height in meters (inches divided by 39.4).2
1Dietary Guidelines, National Institute of Health, 1995
2W. Wayt Gibbs, "Gaining on Fat," Scientific American, Issue #8 1996.