Fitness Articles

Reference Guide to Body Composition

An In-Depth Look at Body Fat, BMI and More

By Jen Mueller and Nicole Nichols, Fitness Experts         
Page 2 of 6

Body Mass Index

What it is: Body Mass Index (BMI) is a quick and easy way to determine, in general terms, if one’s weight is appropriate for one’s height. It has recently been used to quantify an individual's obesity level.

What it measures: Like it says above, BMI helps determine if a person’s weight is within an appropriate range for their height and frame size. It does NOT measure one’s body fat level.

How it works: The equation for BMI is weight (in kilograms) divided by height squared (in meters). To convert pounds to kilograms, divide by 2.2. To convert inches to meters, multiply by .0254. A “healthy” BMI ranges from 18.5 to 24.9.

Where to find it: BMI is commonly used in doctor’s offices, in gyms, and in many weight loss programs. You can use our BMI calculator to find out where you stand.

Accuracy: Since only an individual's height and weight are used, BMI does not provide a differentiation of fat and lean muscle weight. For most adults, however, there is a clear correlation between higher BMI and negative health consequences.

Limitations: BMI is an average that is based on population studies. Because it does not differentiate between fat and nonfat weight, it may overestimate body fat in athletes and others who have a muscular build. In the same way, it may underestimate body fat in older persons and others who have lost muscle mass.

Girth Measurements

What they are: The use of girth and length measurements is a quick, easy and inexpensive method to estimate body composition or describe body proportions. These measures are based on the assumption that body fat tends to be distributed at various sites on the body, such as the waist, neck and thighs, so that is where measurements are often taken. (Muscle tissue, on the other hand, is usually located in places such as the biceps, forearm and calves, which tend to store very little fat.)

What they measure: Some girth measurements use the circumference of various sites on the body to estimate one’s true body fat percentage. Other girth measurements (such as the waist-to-hip ratio) estimate one’s health risk based on these measures.

How they work: Using a cloth tape, girth and length measurements are taken from specific points on the body, such as those described above. The waist-to-hip ratio is one of the most commonly used values to reflect the degree of abdominal obesity.
Continued ›
‹ Previous Page   Page 2 of 6   Next Page ›
Got a story idea? Give us a shout!

About The Author

Nicole Nichols Nicole Nichols
A certified personal trainer and fitness instructor with a bachelor's degree in health education, Nicole loves living a healthy and fit lifestyle and helping others do the same. Nicole was formerly SparkPeople's fitness expert and editor-in-chief, known on the site as "Coach Nicole." Make sure to explore more of her articles and blog posts.

Member Comments

  • Out of these methods, I've tried all but the hydrostatic one (technically tried calipers, but I'm one of those "hard to pinch" people). I seem to get a large range of results. My BMI is 36.6 so I'm apparently really obese, but my waist-to-hip ratio is .804 (under .8 being ideal). Bioimpedance (handheld) testing puts me at 35% body fat. I've also tried some body fat calculators where you enter your measurements, and depending on what measurements are used, I've gotten results anywhere from 28-50%! was the 28%, and it asked for gender, waist, hip, wrist, and forearm measurements. I want to look into the bod pod but first need to find one. - 3/10/2016 10:18:53 PM
  • Clearly by your inaccurate explanation of the bioelectric impedance method you have no idea how it really works. - 8/30/2015 4:26:52 PM
    Handheld bioimpedance machines measure fat in the upper body, scales measure fat in the lower body, both miss the midsection. So if I can balance on my scale with one foot on one side, and one hand on the other, will I get a more accurate reading? :)

    One of these days I'm going to have to actually try that - when nobody is home to see it! - 3/18/2015 8:30:21 AM
  • This and related articles are fine as far as they go. But they are dated and do not go far enough. For example, the World Health Organization recommends an optimal BMI range for HEALTH AND LONGEVITY of 22-18.5 which is based on thorough statistical analysis of mortality and medical cost records.

    This article offers no reasons for targeting any specific body composition. After all, without a target, why consider body composition at all? Additionally, it misses the best body composition method: MRI which is the most accurate and detailed and provides pictures of exactly where body fat is located. Fat location has important health and longevity implications because visceral adipose tissue is a marker for a number of potentially fatal diseases.

    This article needs to be updated. - 4/2/2013 7:28:46 AM
  • This is the best explanation of accurate weight calculations, including BMI, that I have seen in some time. Although it does not account for "shrinkage" as we age (therefore, height and weight may be inaccurate, since the appearance of "body fat" may be in the midsection due to spinal compression), it clearly details the different methods for calculation of accurate weight for height and body habitus. Thank you. - 6/13/2011 12:58:54 PM
  • Now THIS is a thorough discussion of the benefits and problems with various ways to estimate % body fat:


    Interesting that unlike other sources I've read he concludes that DXA is about the same accuracy as hydrostatic weighing. - 3/30/2011 12:44:58 PM
  • Bod Pod is like underwater weighing but less accurate due to the difference in density between water and air. It has all the same sources of error and then some. It's better than no measurement. But circumference measurements are probably better tracking than anything but DXA for most people. - 3/30/2011 12:13:00 PM
  • You really need to update this article to include a reference to DXA body composition scans.

    rgy_X-ray_absorptiometry - 3/30/2011 10:30:22 AM
  • I was wondering about the BodPod machine. I heard that is very accurate. Would like to know more. - 8/30/2010 1:35:47 PM
  • I am reading the book "Racing Weight" by Matt Fitzgerald and he talks about DEXA scanning being a highly accurate way to measure body fat percentage. Before reading this book, I didn't know that. I'm wondering why this method is never mentioned by SparkPeople and not in this article. Getting a DEXA scan can be covered by insurance. - 8/6/2010 4:31:10 PM
  • I've been using a combo of DXA scans every six months and a home body composition scale that's consistently off by the same % (or at least according to the 3 scans I've had done).

    My BMI is normal, now to get the fat down too. - 1/26/2010 5:43:53 AM
  • CLOA513
    Here is link for the DXA body composition mentioned by DEXARED.
    They don't mention the X-ray dose you surely must get with such a scan. Its the cumulative dose that matters so add many DXA scans and some normal X-rays and high community exposure and it would have a significant risk of cancer effect.

    /DEXA.htm - 11/15/2009 10:51:55 PM
  • You can do an easy test in the pool. It is a measurement done for scuba diving and I found it really interesting. Go to the deep end in the water. Take a deep breath and then keep your body upright. A "neutral" body will float with the water at eye level. A body with a lot of fat will float with the water below eye level (for me at my mouth). A body with a lot of muscle will float (or not) below eye level. Of course there are lots of factors like water density that can change the results but I was amazed in my class how quickly they decided what weights people needed to be "neutral" in the water. Cost - admission to a pool. - 8/18/2009 10:01:36 AM
    I am disappointed that you made no mention of DXA (dual energy x-ray absorptiometry) in your analysis of the various body composition methods. This is a very easy, quick and precise way to determine fat and lean mass. The person is measured from head to toe and is a very good way to follow weight loss from one time to another visually showing the entire person. None of the other methods show you an image. This is used by many of the most prestigeous universities and research studies in the country. You missed a very important piece to an otherwise very thurough article. - 7/1/2008 3:28:45 PM
  • Great article. - 6/1/2008 11:37:35 PM

x Lose 10 Pounds by June 11! Sign up with Email Sign up with Facebook
By clicking one of the above buttons, you're indicating that you have read and agree to SparkPeople's Terms & Conditions and Privacy Policy and that you're at least 18 years of age.