Body-Mass Index (BMI)
Waist-to-Height Ratio (WHtR)
Basal Metabolic Rate (BMR)
Body Fat & Surface Area
Willoughby Ideal Weight & Waist

Enter your weight (in lbs), height (in feet and inches), waist (in inches), sex and age. Then, press the Calculate! button.











Body-Mass Index (BMI)


Waist-to-Height Ratio (WHtR)


Body Fat


Basal Metabolic Rate (BMR)


Surface Area


Willoughby Athlete Weight


Willoughby Athlete Waist


Waist is usually measured at one inch above the navel.

Body-Mass Index (BMI)

The body-mass index (BMI) is calculated by dividing your weight (in kg) by the square of your height (in meters). A BMI greater than 25 may indicate that you are overweight, while a BMI greater than 30 generally indicates obesity.

A BMI of 27.8 for men and 27.3 for women is the cutoff point for obesity used in the National Health and Nutrition Examination Survey (NHANES II). The National Academy of Sciences' diet and health report suggests the following normal BMI ranges:


Normal BMI Range

45 to 54 years

22 to 27

55 to 65 years

23 to 28

Over 65 years

24 to 29

(Department of Health and Human Services Consensus Conference on Obesity, April,1 1992)

Dr. Ben Z. Krentzman offers the following interpretation of BMI ranges:

A BMI from 20 through 26: desirable for most middle-aged adults. Nonsmokers with a consistent BMI within this range have the lowest risk of disease and premature death. In this category, weight gain can be avoided through moderate eating habits and exercise.

A BMI from 27 through 29: moderately overweight, carries a slightly increased risk of weight-related health problems, such as high blood pressure, high blood cholesterol, heart disease and adult-onset diabetes. People in this group have the hardest decision to make about reducing, given the potential health risks of weight loss. To prevent the development of weight-related health problems, most people in this category should avoid gaining additional pounds by adopting a low-fat diet and a routine of regular exercise. Weight loss for cosmetic reasons is very common here.

A BMI of 30 through 40: truly overweight, the risk of developing heart disease and other weight-related conditions rises sharply. Most people should lose weight in this category. Adult-onset diabetics in this category should definitely reduce, since blood-sugar control improves with weight loss.

A BMI of 40 or more; severely overweight, you are in great danger of dying early. 80% eat in frequent binges. Secret eating is common. Best weight loss technique is often a fasting diet. Benefits of losing weight clearly outstrip any dangers.

Hamilton and Whitney's Nutrition Concepts and Controversies provides the following interpretation:



 Risk Factor



Underweight. The lower the BMI the greater the risk

 20.7 to 26.4

 19.1 to 25.8

Normal, very low risk

 26.4 to 27.8

 25.8 to 27.3

Marginally overweight, some risk

 27.8 to 31.1

 27.3 to 32.2

Overweight, moderate risk

 31.1 to 45.4

 32.3 to 44.8

Severe overweight, high risk

 > 45.4

 > 44.8

Morbid obesity, very high risk

The National Institutes of Health provided the following guidelines:

Women: Desirable body mass is 21-23. Obesity (20 percent above the desirable range) begins at 27.5. Serious obesity (40% above) begins at 31.5.

Men: Desirable body mass is 22 to 24. Obesity begins at 28.5, and serious obesity begins at 33.

From the National Institutes of Health, June 17, 1998.

People with a BMI of 25 to 29.9 are considered overweight, while those with a BMI of 30 or above are obese.

From Dietary Guidelines provided by the US Department of Agriculture and the Department of Health and Human Services, 2000.

18.5 - 25.0 kg/m2

Healthy Weight

25.0 - 29.9 kg/m2


> 30.0 kg/m2


Waist-to-Height Ratio (WHtR)

The waist-to-height ratio (WHtR) is calculated by dividing your waist size by your height. The WHtR may give a more accurate assesment of health for serious athletes, especially body builders, who have a higher percentage of muscle and a lower percentage of body fat, or for women who have a "pear" rather than an "apple" shape. A WHtR under 50.0% is generally considered healthy.

Current guidelines, as given by the World Health Organization, or the National Heart, Lung and Blood Institute, only give values for waist circumference. Those at substantially increased risk have the same risk as someone with a BMI of 30. Assuming the average male is 5' 9", and the average female is 5' 4", here are the waist cutoff values, and the corresponding WHtR


Increased Risk

Increased Risk

Waist (WHtR)

Waist (WHtR)


37.0" (53.6%)

40.2" (58.3%)


31.5" (49.2%)

34.6" (54.1%)

Here are some values of WHtR that I have come across:



Barbie Doll


Ken Doll


Female College Swimmers


Male College Swimmers


Willoughby Ideal


WHO Increased Risk Females


General Healthy Cutoff


NHANES Risk Equivalent to BMI of 25


WHO Increased Risk Males


WHO Substantially Increased Risk Females


NHANES Risk Equivalent to BMI of 30


Willoughby Obese


WHO Substantially Increased Risk Males


Conclusions about the NHANES data were lifted from Am J Clin Nutr 2002 76 743. An interesting perspective on height-to-waist ratio is provided in Int J Obes Relat Metab Disord. 2003 May; 27(5): 610-6. Also see Prev Med. 2005 Feb; 40(2): 216-20. Hsieh SD, Muto T., The superiority of waist-to-height ratio as an anthropometric index to evaluate clustering of coronary risk factors among non-obese men and women.

As your weight changes, you can expect to lose about 1" from your waistline for each 6-8 lbs of weight loss.

Here's an excellent thesis on the predictive power of Waist-to-Height Ratio for overall fitness written by Captain Steven Swiderski at the Air Force Institute of Technology.

Body Fat

The percentage body fat is calculated for males as 100*(-98.42 + 4.15*waist - 0.082*weight)/weight and for females as 100*(-76.76 + 4.15*waist - 0.082*weight)/weight.

The body fat calculation is based both on weight and waist size, and is exquisitely sensitive to the value for waist. If you lower the value for the weight without changing the waist, the calculation considers this as a loss of muscle mass, and hence the percent body fat goes up. Since it’s difficult to measure waist size accurately, this calculation is not useful when evaluating small changes in body weight.

The percentage of body weight considered "essential fat" is around 4% for men and 10% for women. The American Dietetic Association recommends that men have 15-18% body fat and women have 20-25% body fat. Healthy male athletes might be as low as 5-12% body fat, and healthy female athletes could be as low as 10-20%. The American Council on Exercise recommends men's body fat should be 6-25%, and women's should be 14-31%.

Basal Metabolic Rate (BMR)

The basal metabolic rate is calculated according to equations given by Harris and Benedict.

For men: BMR = 13.75 weight(kg) + 5.003 height(cm) - 6.775 age + 66.5.
For women: BMR = 9.563 weight(kg) + 1.850 height(cm) - 4.676 age + 655.1.

Harris J, Benedict F. A biometric study of basal metabolism in man. Washington D.C. Carnegie Institute of Washington. 1919.

The basal metabolic rate is your energy expenditure without any contribution from exercise or digestion. Another term used is the resting energy expenditure (REE), which may also include energy used in digesting food.

Generally, it is inadvisable to ingest fewer calories than your basal metabolic rate. Note that BMR is given in kcals/day. The usual term of calories in food actually refers to kilocalories.

Thanks to Phil Weaver of Houghton, Cumbria, UK for alertly pointing out an error in an earlier version of this page. If you used the BMR calculation prior to January 31, 2005, you may want to redo the calculation.

Surface Area

The body surface area is calculated as sqrt (height x weight / 3131), the Mosteller formula, with the weight in lbs and the height in inches. Prior to May 1, 2006 there was a mistake in this calculation that was spotted by Deborah Byatt. If you're interested in many other surfaced area calculations, see Dr. Hall's page.

Willoughby Athlete Weight and Waist

The Willoughby athlete weight is calculated by dividing the cube of the height (in inches) by 1906 [Thanks to Konrad Balcerak for spotting a mistake in the text prior to August 2006]. The Willoughby athlete waist is calculated by multiplying the height by 0.4584.

David P Willoughby, who was a champion body builder in the early twentieth century, performed extensive anthropometrics measurements on highly-conditioned (male) athletes and found a direct proportionality between waist and height. His ideal form had a WHtR of 45.8%. Willoughby also tabulated data for the morbidly obese, and found the same proportionality between waist and height, but with a WHtR of 57.7%.

Interestingly, although in the Metropolitan Life Tables the weight values are proportional to the square of the height (in accordance with the calculation of Quetelet's Index or BMI), in Willoughby's data the weights are proportional to the cube of the height (in accordance with Rohrer's Index).

The Willoughby athlete weight is then the average ideal weight for male athletes; strength-trainers may weigh more, while endurance athletes will weigh less. Are you a Willoughby athlete? A check on this is to compare your waist measurement to the Willoughby athlete waist calculation.

Other pages by the author. Please send comments on this page to Jeffrey Clymer.
Revision No. 18. December 28, 2012. Visitors:

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