This BMI Calculator for men and women is easy to use and gives you information about your body mass index. Your body mass index or BMI is a measurement that uses both your weight and your height. There are different 4 weight categories - underweight, healthy, overweight and obese.
Body Mass Index (BMI) – The Complete Guide
Table of Contents
- Body Mass Index (BMI) – The Complete Guide
- 1. What is the Body Mass Index (BMI)?
- 2. What is the Body Mass Index Used for?
- 3. Global Body Mass Index Statistics vs. South Africa
- 4. Possible Limitations of the BMI
- 5. Alternative Measures to BMI
- 6. The Benefits of Keeping a Healthy Weight
- 7. Body Mass Index – The Final Word
The most recent obesity statistics from the World Health Organization (WHO) make grim reading. The WHO published an updated list of statistics in February 2018 and found that global obesity has tripled since 1975. There are now 1.9 billion overweight adults around the world, 650 million of whom are obese.
The terms ‘overweight’ and ‘obese’ are defined as “abnormal or excessive fat accumulation that may impair health” by the WHO. In other words, aesthetics doesn’t enter the equation; carrying too much weight is bad for your health. There are numerous tools used to calculate whether or not a person is overweight. Even with the advances in medical technology, the Body Mass Index (BMI) is one of the most frequently used measurements of a person’s physical shape and general health, some 150 years after it was first conceived.
1. What is the Body Mass Index (BMI)?
The body mass index, occasionally called the Quetelet index, is a value taken from a person’s height and weight. It is also determined via a BMI chart table and is an attempt to quantify the level of tissue mass (comprised of bone, fat, and muscle) in a person.
The result is used to determine if that individual is obese, overweight, normal weight or underweight depending on where they fall within the BMI category ranges.
1.1 How is BMI Calculated?
The body mass index formula is easy to determine. It’s a simple calculation that takes into account your weight and height.
- The imperial BMI formula = Weight (LBS) x 703 ÷ Height (Inches²)
- The metric BMI formula = Weight (KG) ÷ Height (Metres²)
If you wish to calculate your BMI using the imperial system, here’s the height and weight conversion figures:
- 1 kilogram = 2.2 pounds
- 1 foot = 12 inches
- 1 inch = 2.54 centimetres
If you are 5ft 4 inches by the imperial system, you are 162.56cm or 1.63m (rounded up) by the metric system.
Example BMI Calculations
Example 1: This is how to calculate your body mass index score if you were to weigh 209 pounds and are 6 feet 2 inches tall.
- 209 pounds = 95 kilograms
- 6 feet 2 inches = 1.88m
- 1.88 x 1.88 = 3.53
- 95/3.53 = 26.91
The BMI Score in this case = 26.91.
Example 2: Some countries use an entirely different calculation to reach the same result.
Weight in pounds / your height in inches squared x 703
Using the same example as before, you calculate as follows:
- (209 / 74 x 74) x 703 = (209 / 5,476) x 703
The BMI Score in this case = 26.83.
Why the difference? Because there is a certain element of ‘rounding up’ or ‘rounding down’ involved e.g. 26.784 becomes 26.78 and so on.
But where does this place you on the BMI category chart? In the next section we cover the bmi categories and explain the classifications.
1.2 Body Mass Index Categories
Technically, the BMI scale will place you in one of six categories. The table below lists the BMI categories along with the BMI score associated with each category.
|Classification||Body Mass Index Score|
|Underweight||less than 18.5|
|Normal Weight||18.5 – 24.9|
|Overweight||25 – 29.9|
|Obesity (Class 1)||30 – 34.9|
|Obesity (Class 2)||35 – 39.9|
|Extreme Obesity (Class 3)||40+|
The following body mass index chart allows you to manually get your BMI score and includes a classification of the BMI category you reside within.
1.3 BMI for Children
Although the BMI calculator works in the same way for children, the measurement is used differently. While the BMI ranges remain the same for adults throughout their life, these figures change in children because kids are still growing and do so at different rates. As a result, BMI is a measure of weight for height compared to children of the same age. This calculation results in a body mass index percentile.
For instance, if your child is in the 50th percentile, it means that 50% of children of the same age have the same BMI figure or less. The 85th percentile means that 85% of kids have the same or lower BMI and this is a figure where your child is classified as being ‘at risk’ of becoming overweight. At the 95th percentile, your child is classified as ‘overweight’.
Example: If your child is a 14-year-old boy who is 5ft 3 inches tall and weighs 120 pounds for example, his BMI is 21.3 which puts him in the 76th percentile. This BMI figure indicates that he is at a healthy weight because the proper range is between 90 and 128 pounds in this instance.
Here is what that reading looks like when based on BMI percentiles.
1.4 BMI Charts
Body Mass Index charts are useful for visualizing the ranges associated with each BMI category. You can use them to easily locate your height and weight to determine your BMI score and the associated BMI category you fit within.
BMI Chart for Adults (Men & Women)
BMI Chart for Kids & Teens (Boys)
The Body Mass Index is sometimes called the Quetelet Index after its creator, a Belgian mathematician, astronomer, sociologist, statistician and all-around genius named Lambert Adolphe Jacques Quetelet. He came up with the idea sometime between 1830 and 1850 as part of his development of ‘social physics’.
Even so, it was seldom used and only started to become popular in the latter part of the 20th century. The term Body Mass Index was first coined by Ancel Keys and other authors of a paper published in the Journal of Chronic Diseases in July 1972. According to the paper, BMI was “at least as good as any other relative weight index as an indicator of relative obesity.” At least Keys acknowledged that it was “not fully satisfactory.”
Prior to the 1980s, physicians used weight for height tables which differed according to gender. It was during this decade that the BMI calculator became the international standard for obesity measurement. Once governments around the world began noting the obesity problem in society, and started launching healthier lifestyle initiatives, the public at large became aware of BMI.
Initially, the threshold for being overweight was 27.8 but it was lowered to 25 internationally. In 1998, the United States National Institutes of Health followed suit and also reduced the BMI figure. This move resulted in 30 million Americans becoming classified as overweight overnight!
2. What is the Body Mass Index Used for?
Even though the Body Mass Index is over 150 years old, major health authorities such as the CDC and NIH in the United States still believe it is a ‘fairly reliable indicator of body fatness for most people.’
2.1 Public Health Statistics
Even today, BMI is used as the official measure of national obesity rates. For instance, the European Union continues to use it as a yardstick for the obesity epidemic and also suggests that people with higher BMI are at greater risk of diseases such as hypertension, cancer, and cardiovascular disease.
According to the Harvard T.H. Chan School of Public Health, your risk of developing conditions such as type-2 diabetes increases progressively as your BMI rises above 21.
2.2 Weight Range Analysis
The BMI range is also considered to be an accurate measure of your weight range. Therefore, if you have a BMI of 27, you are considered overweight regardless of what you actually weigh and your body composition or gender is not taken into account.
2.3 Screening Tool for Weight Problems
If a physician calculates a higher than normal BMI, the next step is to see if you are at risk of certain health problems. In fact, the main purpose of BMI is to determine whether you’re likely to develop a serious medical problem later in life.
In France for example, BMI is used as a screening tool for child malnutrition. The CDC champions the BMI scale as an effective means of determining whether children and teenagers are underweight, overweight, or obese.
2.4 Fashion Industry
The fashion industry’s obsession with exceedingly thin models has ensured that the BMI calculator has a permanent home there. The industry is constantly under fire for forcing women, in particular, to attain what the UK Women’s Equality Party calls “an unattainable level of thinness in women.” The party has called on all models with a BMI below 18.5 to be seen by a physician from an accredited list who will decide if that woman is healthy enough to work.
There is a law to that effect in Israel where male and female models with a BMI under 18.5 much obtain a medical certificate confirming a ‘normal’ BMI reading. For reference, Kate Moss, one of the most famous models ever, had a BMI of just 15 at the height of her fame. By any measure, including BMI, she was severely thin.
3. Global Body Mass Index Statistics vs. South Africa
BMI measurements vary around the globe and some nations have a greater ‘obesity’ problems than others according to the BMI scales. For a better understanding of global BMI scores, we have compiled statistics from six regions globally. First of all, here is the average body mass of people in different continents expressed in kilograms:
|Region||Average Body Mass (KGs)|
|Latin America / Caribbean||67.9 kg|
|North America||80.7 kg|
|Global Average||62.0 kg|
As you can see, Asians are significantly lighter than Americans for example and while they are shorter on average, it is evident that residents in North America have a higher BMI figure.
3.1 Overview of BMI Statistics in South Africa
South Africa’s average BMI is 26.3 which places it just outside the top 30 in the world but it also has one of the biggest disparities between men and women.
3.2 Average BMI of South African Males
South African men are within the normal range with an average BMI of 24.3, a figure that places the nation outside the top 50.
3.3 Average BMI of South African Females
In contrast, the average BMI of South African women is extremely high at 28.2, a figure that positions it in the world’s top 20 highest BMI averages.
3.4 Obesity Rates in South Africa
As the BMI statistics show, obesity is a major problem amongst South African women. According to World Obesity, 41% of females aged 15+ are obese in South Africa, compared to just 11% of males.
4. Possible Limitations of the BMI
The Body Mass Index has its fair share of detractors. It has been derided as a flawed measurement tool. The following 4 points are often highlighted.
4.1 Age & Sex
There is a significant difference in body composition between the sexes and this isn’t taken into account by BMI calculators. Male BMI and female BMI measurements should be different because women tend to have a higher percentage of body fat. While men have little more than 2-5% essential body fat, women have 10-13%. Therefore, if a male and a female both have a BMI of 28, they are not equally overweight.
It is sadly also a fact that we lose muscle mass as we get older. Therefore, if you have the same BMI of 23 at age 65 as you did when you were 35, it doesn’t mean you are at a ‘healthy’ weight. You almost certainly have more body fat at 65 so you’re more likely to be overweight.
4.2 Physical Characteristics
The BMI calculator also exaggerates obesity in taller people and thinness in shorter people. For example, a two-meter tall man who weighs 104 kilograms is classified as ‘overweight’ according to the BMI scale (104 / 4 = 26).
In contrast, someone who is 1.5m tall and weighs 54 kilograms has a BMI of 24 (54 / 2.25) and is classified as ‘normal’ weight even though they are possibly overweight in real terms.
The fact of the matter is this: There were no calculators or computers during the 19th century so Ouetelet devised a system limited by the age he lived in. It is remarkable that over 150 years later, with so much technology at our fingertips, that medical professionals still use such an outdated system.
4.3 Weight vs. Body Fat
It is likely that BMI underestimates obesity, especially in the United States. In America, around one-third of the population are obese by BMI standards but other measurements suggest the true figure is closer to 60%.
Research conducted by Tomiyama et al. and published in the International Journal of Obesity in 2015, looked at the misclassification of cardiometabolic health when using BMI as a measuring stick. The team analyzed a group of participants over a seven-year period and made some startling discoveries. They found that 54 million Americans had been classified as obese or overweight through the Body Mass Index but cardiometabolic measurements showed them to be healthy. Meanwhile, 21 million people were deemed ‘normal’ in BMI terms but were actually unhealthy.
The fact that BMI uses your weight as its primary measuring tool means it is inaccurate. The density of your bone structure alone will throw off BMI calculations so a big-boned individual could wrongly be told that they are obese and at greater risk of medical conditions such as diabetes and stroke.
4.4 Athletes & Sports Professionals
BMI is usually NOT used for bodybuilders, sprinters, long distance runners or anyone else classified as a professional athlete or sportsperson. That’s because these individuals tend to have a higher rate of muscle mass which skews the figures. In the case of endurance athletes, a lack of muscle mass can also produce misleading results.
A prime example would be an Olympic sprinter who could have a BMI of 27; the same as an unfit couch potato. According to the BMI scale, both individuals are overweight even though one is a world class athlete and the other is an extremely unhealthy sedentary person.
5. Alternative Measures to BMI
5.1 Body Fat Percentage
A person’s body fat percentage is considered by some to be a better representation of their overall health than the BMI scale. It is simply a measurement of how much fat you’re carrying.
Example: a 180-pound male with 36 pounds of fat has a body fat percentage of 20%. Simply multiply the amount of fat you have by 100 and divide by your total weight:
36 x 100 = 3600
3600 / 180
Unlike the BMI scale, body fat percentage takes into account the differences between men and women. Here is the chart according to the American Council on Exercise:
|Classification||Male Body Fat Percentage||Female Body Fat Percentage|
As you can see, women tend to get 6-8% leeway on account of holding that much extra in essential fat. The Jackson and Pollock formula uses body fat percentage chart based on gender and age. For example, a 20-year-old male will ideally have 8.5% body fat but this figure rises to 20.9% aged 55.
There is special body fat percentage machines where you just stand on them and allow a mild electrical current to course through your body. You can also use the old-fashioned yet accurate calipers method. Simply measure the skin folds on specific points on the body to come up with a body fat % figure.
If you look at the charts above, you’ll see that a 27-year old woman with a calipers measurement of 12 millimeters is classified as ‘ideal’ with a body fat percentage of around 22-23%.
5.2 Waist to Hip Ratio
Other physicians believe that a person’s waist-to-hip ratio is an even better measure of health. According to a study published in PloS Magazine, waist circumstance is strongly linked to type 2 diabetes risk even after BMI is taken into account.
Researchers discovered that a non-obese but overweight man (in BMI terms) with a waist size of 102 cm or more (40.2 inches) has at least the same risk of type 2 diabetes as an obese male. The same situation applies to females with a waist size of 88 cm or more (34.6 inches).
Your waist-to-hip ratio is one of the best indicators of future disease risk because a higher ratio suggests that you have a high level of harmful visceral fat. This is the fat that accumulates around the internal organs and if you have too much of it, the result could be the release of hormones and proteins that lead to inflammation. This in turn damages arteries, enters your liver and impacts how the body breaks down fats and sugars.
|Classification||Male Waist-to-Hip Ratio||Female Waist-to-Hip Ratio|
|Low Risk||0.81 – 0.95||0.71 – 0.8|
|Moderate Risk||0.96 – 0.99||0.81 – 0.84|
Therefore, a man with 40-inch hips should ideally have a 32-inch waist (32 / 40 = 0.8).
A simpler version to judge your waist-to-height ratio is to keep your waist size to less than half of your height to reduce the risk of type 2 diabetes. Therefore, a 6-foot tall man (72 inches) should have a maximum waist measurement of 36 inches.
6. The Benefits of Keeping a Healthy Weight
6.1 Why Maintaining a Healthy Weight is Important
There is a lot more to keeping your weight in the ‘healthy’ range than merely looking good. It is a critical component of general health as it reduces your risk of developing serious medical conditions. If you’re overweight, it can be as simple as eating less and moving more. If you’re underweight, perhaps you should exercise less or eat a little more.
6.2 The Dangers of Being Overweight
Once you enter ‘overweight’ territory on the BMI scale, you will be at greater risk of a host of serious medical conditions.
In postmenopausal women, the risk of getting breast cancer increases by 20-40% when overweight according to a study by Munsell et al. published in 2014. Excess abdominal fat increases your risk by 43%.
Experts in the field suggest that a BMI of between 20 and 24 is the perfect zone for fertility. Up to 12% of fertility problems stem from weight problems (being overweight or underweight). In women, weight impacts periods and ovulation.
A study published in the Journal of the American College of Cardiology in April 2014 researched almost 15,000 Korean adults with no known case of heart disease. The team discovered that people with a BMI of over 25 were at greater risk of having early plaque buildup in their arteries than people at a ‘normal’ weight.
Type 2 Diabetes
According to WHO research entitled Global Report on Diabetes, up to 422 million adults were living with diabetes in 2014. This is almost quadruple the 1980 figure of 108 million. In that time, the rate of obesity has also risen. Recent research suggests that obesity accounts for up to 85% of the risk of developing type 2 diabetes. If you are obese, you are 80 times more likely to develop diabetes than someone with a BMI of 22 or less.
A 2012 study by the Johns Hopkins University School of Medicine showed a link between weight loss and better sleep. The six-month study was led by professor of medicine, Kerry Stewart, Ed. D, and involved 77 volunteers with pre-diabetes or type 2 diabetes. All 77 participants were either obese or overweight and were assigned to one of two groups. Group A went on a weight-loss diet and exercise regime. Group B only benefitted from the diet portion. Both groups lost 15 pounds and 15% of belly fat on average. What’s more, both groups improved their overall sleep score by 20%.
Reduced Life Expectancy
This is unquestionably the biggest danger of being overweight or obese. According to the Organization for Economic Co-operation and Development, your risk of death increases by 30% for every 33 pounds of excess weight you carry. A severely obese individual (someone with a BMI of 40+) can expect to live 8-10 years less than a person in the ‘normal’ BMI range.
6.3 The Dangers of Being Underweight
With such an emphasis on losing weight, it is easy to overlook the fact that being underweight also increases your risk of declining health. That’s one of the reasons why protest groups are so unhappy with the fashion industry. You fall into the ‘underweight’ category if your BMI is below 18.5.
According to the CDC, as at 2014, an estimated 1.4% of American adults are underweight. However, as this issue isn’t as well researched as obesity, there is a fairly high margin of error in the study. Here are some of the health risks associated with having an extremely low BMI score:
Contrary to what you may believe, malnutrition does not relate to eating or drinking too little. In reality, it is a term used to describe an insufficient intake of nutrients. If you don’t eat enough to fuel your body, symptoms can include fatigue and hair loss.
Decreased Immune Function
A review of the risk of infection in people with high and low BMI scores was published by Dobner and Kaser in January 2018. The review found that there was a notable connection between being underweight and increased infections. Malnourishment can reduce your immune system strength which means you’re less able to ward off infections and diseases.
A 2016 study by Lim and Park found that in premenopausal women, 24% of those with a BMI below 18.5 had low bone mass density. In contrast, only 9.4% of women with a BMI above 18.5 had the same issue.
Increase of Surgical Complications
In one study, underweight people who had total knee replacement surgery were at greater risk of infection afterward than people of a normal weight.
7. Body Mass Index – The Final Word
While it is true that there are a few concerns about BMI, it is still the most tried and trusted way to ascertain the average person’s general health. It is one of the quickest and easiest methods of determining whether you need to lose/gain weight and change your lifestyle. We recommend that you find out your BMI as soon as possible and if it is above or below the average range, book an appointment with your physician and seek advice. This simple test could prevent serious health issues going forward.
If your BMI is over 25 or below 18.5, you should conduct a body fat percentage test and also look at your waist-to-hip and waist-to-height ratios. A combination of all these measurements, plus an honest look in the mirror, should help you determine whether you need to lose or gain weight.
What isn’t in doubt is the growing levels of obesity around the world. The average BMI score of dozens of nations is in the overweight category and there are genuine fears that within a generation or two, there will be more obese people than non-obese.
It is a combination of longer working hours, easy access to cheap processed foods, and a lack of desire to exercise that is responsible for the current obesity epidemic. It would behoove nations in Europe, Oceania and North America, to look at the example set by countries in the Far East of Asia such as Japan which has an average BMI of 22.5, almost directly in the center of ‘normal’. Reduced consumption of processed foods and reliance on fresh fish, fruit, and vegetables ensures that Japan is one of the world’s healthiest nations.
For the record, there is unquestionably a link between BMI and wealth globally. Most of the countries with the lowest BMI averages are among the poorest on the planet. They include Bangladesh (20.2), Eritrea (20.2) and Ethiopia (20.3).
Meanwhile, several of the world’s wealthiest countries have the highest BMI averages. They include Kuwait (29.5), USA (28.8), and the United Arab Emirates (28). Unfortunately, when we revisit these statistics in a decade or so, the average BMI of most countries will have increased and at least one will enter the ‘Obese’ zone of 30 as an average.
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