The Body Mass Index (BMI) Interpreted calculator uses the body mass index to provide a short interpretive body mass statement.
INSTRUCTIONS: Choose units and enter the following:
- (H) Height
- (W) Weight
- (G) Gender (male, female)
BMI Interpretation: The calculator returns the BMI with the annotated interpretation.
The Math / Science
The Body Mass Index (BMI) is typically calculated using kilograms (kg) for one's weight (mass) and their height in meters (m). vCalc allows the user to enter other units (e.g. inches and pounds) via the pull down menu. vCalc converts the different units to kilograms and meters, calculates the BMI, and then provides the nominal assessment.
The interpretation is based on the following guideline for men and women:
| BMI for Men | BMI for Women | Interpretation | |
| < 17.5 | <17.5 | anorexia | |
| 20.7 | 19.1 | underweight | |
| 26.4 | 25.8 | in normal range | |
| 27.8 | 27.3 | marginally overweight | |
| 31.1 | 32.3 | overweight | |
| 35 | 35 | obese | |
| 40 | 40 | severely obese | |
| 50 | 50 | morbidly obese | |
| more | more | super obese |
Limitations and shortcomings:
This graph shows the correlation between body mass index (BMI) and percent body fat (%BF) for 8550 men in NCHS' NHANES 1994 data. Data in the upper left and lower right quadrants show some limitations of BMI.[26]The medical establishment[27] and statistical community[28] have both highlighted the limitations of BMI. Because the BMI depends upon weight and the square of height, it ignores basic scaling laws whereby mass increases to the 3rd power of linear dimensions. Hence, larger individuals, even if they had exactly the same body shape and relative composition, always have a larger BMI.[29] Also, its assumptions about the distribution between lean mass and adipose tissue are inexact. BMI generally overestimates adiposity on those with more lean body mass (e.g., athletes) and underestimates excess adiposity on those with less lean body mass. A study in June 2008 by Romero-Corral et al. examined 13,601 subjects from the United States' third National Health and Nutrition Examination Survey (NHANES III) and found that BMI-defined obesity (BMI > 30) was present in 21% of men and 31% of women. Using body fat percentages (BF%), however, BF%-defined obesity was found in 50% of men and 62% of women. While BMI-defined obesity showed high specificity (95% for men and 99% for women), BMI showed poor sensitivity (36% for men and 49% for women). Despite this undercounting of obesity by BMI, BMI values in the intermediate BMI range of 20–30 were found to be associated with a wide range of body fat percentages. For men with a BMI of 25, about 20% have a body fat percentage below 20% and about 10% have body fat percentage above 30%.[26]
Mathematician Keith Devlin and the restaurant industry association Center for Consumer Freedom argue that the error in the BMI is significant and so pervasive that it is not generally useful in evaluation of health.[30][31] University of Chicago political science professor Eric Oliver says BMI is a convenient but inaccurate measure of weight, forced onto the populace, and should be revised.[32]
A study published by Journal of the American Medical Association (JAMA) in 2005 showed that overweight people had a similar relative risk of mortality to normal weight people as defined by BMI, while underweight and obese people had a higher death rate.[33] High BMI is associated with type 2 diabetes only in persons with high serum gamma-glutamyl transpeptidase.[34]
In an analysis of 40 studies involving 250,000 people, patients with coronary artery disease with normal BMIs were at higher risk of death from cardiovascular disease than people whose BMIs put them in the overweight range (BMI 25–29.9).[35] In the overweight, or intermediate, range of BMI (25–29.9), the study found that BMI failed to discriminate between bodyfat percentage and lean mass. The study concluded that "the accuracy of BMI in diagnosing obesity is limited, particularly for individuals in the intermediate BMI ranges, in men and in the elderly. These results may help to explain the unexpected better survival in overweight/mild obese patients."[26]
A 2010 study that followed 11,000 subjects for up to eight years concluded that BMI is not a good measure for the risk of heart attack, stroke or death. A better measure was found to be the waist-to-height ratio.[36] A 2011 study that followed 60,000 participants for up to 13 years found that waist–hip ratio was a better predictor of ischaemic heart disease mortality.[37]
BMI is particularly inaccurate for people who are very fit or athletic, as their high muscle mass can classify them in the overweight category by BMI, even though their body fat percentages frequently fall in the 10–15% category, which is below that of a more sedentary person of average build who has a normal BMI number. Body composition for athletes is often better calculated using measures of body fat, as determined by such techniques as skinfold measurements or underwater weighing and the limitations of manual measurement have also led to new, alternative methods to measure obesity, such as the body volume index. However, recent studies of American football linemen who undergo intensive weight training to increase their muscle mass show that they frequently suffer many of the same problems as people ordinarily considered obese, notably sleep apnea.[38][39]
BMI also does not account for body frame size; a person may have a small frame and be carrying more fat than optimal, but their BMI reflects that they are normal. Conversely, a large framed individual may be quite healthy with a fairly low body fat percentage, but be classified as overweight by BMI. Accurate frame size calculators use several measurements (wrist circumference, elbow width, neck circumference and others) to determine what category an individual falls into for a given height. The standard is to use frame size in conjunction with ideal height/weight charts and add roughly 10% for a large frame or subtract roughly 10% for a smaller frame.[citation needed]
For example, a chart may say the ideal weight for a man 5 ft 10 in (178 cm) is 165 pounds (75 kg). But if that man has a slender build (small frame), he may be overweight at 165 pounds (75 kg) and should reduce by 10%, to roughly 150 pounds (68 kg). In the reverse, the man with a larger frame and more solid build can be quite healthy at 180 pounds (82 kg). If one teeters on the edge of small/medium or medium/large, a dose of common sense should be used in calculating their ideal weight. However, falling into your ideal weight range for height and build is still not as accurate in determining health risk factors as waist/height ratio and actual body fat percentage.
A further limitation of BMI relates to loss of height through aging. In this situation, BMI will increase without any corresponding increase in weight.
The exponent of 2 in the denominator of the formula for BMI is arbitrary. It is meant to reduce variability in the BMI associated only with a difference in size, rather than with differences in weight relative to one's ideal weight. If taller people were simply scaled-up versions of shorter people, the appropriate exponent would be 3, as weight would increase with the cube of height. However, on average, taller people have a slimmer build relative to their height than do shorter people, and the exponent which matches the variation best is less than 3. An analysis based on data gathered in the US suggested an exponent of 2.6 would yield the best fit for children aged 2 to 19 years old.[10] For US adults, exponent estimates range from 1.92 to 1.96 for males and from 1.45 to 1.95 for females.[40][41] The exponent 2 is used by convention and for simplicity.
References:
- Wikipedia - http://en.wikipedia.org/wiki/Body_mass_index
- Body Composition
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- LBMW - Lean Body Mass for Women based on height and weight
- LBMM - Lean Body Mass for Men
- BMI - Body Mass Index with interpretation
- CREFF - Ideal Weight Calculator using bone size (morphology)
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Additional Resources:
Check out the Heart Heath Calculator and the Metabolic Health Calculator for more Health and Fitness Equations.