BMI: calculator, chart, healthy range for men and women

What is body mass index?

BMI (a body mass index) is a value stemming from the weight and height of a person, which categorizes a person’s mass. Specifically, BMI is body mass in kilograms divided by the square of height in meters and the BMI value is expressed in a unit of kg/m².  BMI was created at the beginning of the XIX century as a tool for measuring the average weight of people. Nowadays, it is still the most simple and inexpensive device for determining the weight category. It allows for estimating the serious health conditions, especially obesity or underweight, and serves as an indicator for further examination of a patient’s health. BMI calculators and tables may be used by everyone and the tables or charts available on the Internet are clear enough to categorize oneself, however, doctors also make great use of BMI while assessing the health condition of adults as well as young patients. 

BMI is the easiest way to determine the weight category. It allows for estimating the serious health conditions like obesity or underweight

What is BMI used for?

BMI indicator is used for determining the category to which a person belongs according to the mass/height relation.

The 4 main categories include underweight, healthy weight, overweight, and obese.

The WHO presents the detailed ranges of values that suit given categories:

• very severely underweight: BMI less than 15
• severely underweight: BMI of 15-16
• underweight: BMI of 16-18,5
• healthy weight (normal): BMI of 18,5-25
• overweight: BMI of 25-30
• class 1 obesity (moderately obese): BMI of 30-35
• class 2 obesity (severely obese): BMI of 35-40
• class 3 obesity (morbidly obese): BMI over 40

BMI defines the anthropometric weight and height characteristics and categorizes them into groups. Generally speaking, the body mass index represents a person’s fatness level. The most important asset of BMI is that it allows for determining people who are severely underweight and overweight because these are very serious health conditions that often require medical help.

How do you calculate body mass index?

Generally, there is one method of calculating BMI for adults and children.

Below, we illustrate the calculation of BMI for people using such measurement units as meters/kilograms and inches/pounds.

1. Using meters and kilograms as units for measurements

Formula: [weight given in kilograms] / [height given in meters]²

As shown, in this system, the BMI formula is calculated by weight in kilograms divided by squared height in meters.

Usually, height is measured in centimeters, so it needs to be converted to meters.

For example: weight 70kg, height 172cm (1,72m)

BMI = 70 ÷ (1,72)²

BMI = 23,66

 2. Using inches and pounds as units for measurements

Formula: [weight in pounds (lb)] / [height in inches]² x 703

BMI formula is calculated by dividing weight in lbs by squared height in inches and multiplying by 703.

For example: weight 165lbs, height 66″

BMI = 165 ÷ (66)² x 703 

BMI = 26,63

It may seem complicated to calculate BMI, however, after reading the formulas, it becomes rather clear. However, nowadays there are hundreds of automatic BMI calculators where people only insert their weight, height (and alternatively sex and age), and their BMI is calculated in a second.

What is a good body mass index?

BMI helps control body mass and allows people to start acting early enough to avoid health problems in the future

Measuring the BMI allows for indicating if a person is overweight or obese. Of course, from the medical point of view, there needs to be some other measurements and tests taken to determine the patient’s condition. However, BMI is usually the first indicator of weight problems. 

There is a significant relation between certain health conditions and diseases and excess weight.

The most common issues caused by obesity/overweight and related to it are:

• type 2 diabetes
• hypertension
• stroke
• coronary heart disease
• sleep apnea
• respiratory problems
• osteoarthritis
• some types of cancers.

People are advised to check themselves what is a good body mass index and what should your body mass index should be. It helps control body mass and allows people to start dieting and exercising early enough to avoid these health problems in the future. 

A person with a good BMI, which ideally is between 18,5 and 25, may benefit from:

• a satisfying physical look
• no joint or muscle pain
• well regulated body fluids
• normal blood pressure
• a good sleep
• low risk of heart or liver disease
• no problems with sugar level.

What is more, BMI is strongly related to body fatness, however, there are some exceptions to this rule. For instance, women, in general, have more fat than men with the same BMI, older people have more fat than young people with the same BMI, athletes have a minimum fat percentage while their BMI is often very high. It is also worth mentioning that BMI is greatly accurate for people who have much fat and thus are overweight or obese. 

What is a healthy BMI for a woman and what is a healthy BMI for men?

Generally, the BMI ranges and categories for women and men are identical. So, BMI of 18-25 is a range showing what is a good BMI for men and what is a good BMI for a woman? Any deviations (lower or higher BMI), should make men and women think whether their lifestyle is healthy or they need to make some changes in diet and exercise. 

However, what distinguishes men and women is the body fat range. Too much excess fat leads to type 2 diabetes, stroke, or heart diseases while too little fat is a sign of malnutrition. The right percentage of fat in the body helps the vitamin and mineral intake, regulates body temperature, protects the organs, and most importantly, is a source of energy.

The healthy fat ranges are as follows:

The table shows clearly that women have more fat than men – as a result, the BMI of women is often higher than of men, but it stems from pure physiology.

What is a healthy BMI for a child?

The body mass index for children aged 2-18 is measured according to weight, height, age, and gender – such a categorization is necessary because children or teenagers grow up and change physically differently depending on their age and gender. The scale for children’s BMI is extended by age and sex, and the final outcome is measured in percentiles.

The BMI groups and ranges are as follows:

• underweight (2nd centile or less)
• healthy weight (from 2nd centile to 85th centile) 
• overweight (from 85th to 95th centile)
• very overweight (over 95th centile)

BMI tool can help parents, teachers, and doctors to help children maintain a healthy weight and react when the weight is too high or too low

Nowadays, the problem of obesity among children and teenagers is getting worse and worse especially in the USA and Western European countries. Hence, it is of uttermost importance to pay attention to children’s eating habits and encourage them to practice sport. BMI is a tool that may help parents, teachers, and doctors to help children maintain a healthy weight and react when the weight is too high or too low. Besides, parents must realize that the eating habits and attitude towards a healthy lifestyle in general, is shaped in the childhood, so any weight problems of children are caused by parents’ mistakes to a great extent. 

What BMI qualifies for weight loss surgery?

Weight loss surgeries are performed to obese people who have tried losing weight by a healthy diet and exercising, but with no effects. Obesity is a disorder that is very dangerous and at some stage becomes morbid, it also triggers some related health conditions, so the bariatric surgery in this case simply saves a patient’s life. The most common bariatric surgeries are gastric sleeve, gastric bypass, and gastric balloon. There are certain criteria for each of these surgeries that must be met to get qualified for the surgery and depending on the surgery type they may slightly differ. 

However, the general criterion of BMI for weight loss surgery is:

• BMI over 40 (usually patients with BMI of 40 or higher are qualified for a bariatric surgery)
• BMI between 35 and 40 (usually patients with this BMI are qualified for a bariatric surgery only when they suffer from obesity-related conditions e.g. type 2 diabetes or high blood pressure).

It is also worth mentioning that if patients have a BMI over 50, they may be disqualified from the surgery and asked to lose weight (so that the BMI is below 50) before they are qualified. The reason for that is too high risk of death during the general anesthesia and difficulty in performing the surgery due to the excessive fat around the organs. On the other hand, sometimes people with BMI below 35 may be qualified because they struggle with serious health conditions resulting from their excessive weight. If people have any doubts about BMI requirements for bariatric surgery or whether they have a suitable BMI for bariatric surgery, it is always good to contact a GP and ask about BMI guidelines for bariatric surgery and steps towards such procedures.

BMI chart

BMI is clearly determined with the use of a table or BMI chart showing the categories and BMI ranges. Such charts are available on the Internet as well as at the doctor’s offices and are widely used by professionals as well as non-professionals. 

The example of such a chart is as follows:

We would like to mention here that the BMI indicator is very important in the general, first diagnosis, but it is not a totally perfect measurement.

The problem with BMI is:

• it does not distinguish between skeletal, fat, and muscle tissues or fluid percentage, so there may be some misconceptions regarding the BMI category. It is clearly illustrated in athletes BMI – which often indicated that they are overweight or obese, while most of their weight components are the muscles, not fat;
• BMI indicating obesity or overweight doesn’t mean that the person is unhealthy. Here, the cardiometabolic profile of a person matters, and the statistics show that about 50% of overweight people and up to 30% of obese people have a healthy cardiometabolic profile
• behaviors and habits are more important than BMI – people may have a low BMI, but at the same time smoke cigarettes, drink alcohol and eat fast foods regularly – it makes more hurt to their organisms than a higher BMI of a person who eat healthily;
• some amount of fat is essential for our bodies – people should not strive for getting as low BMI as they can.

BMI calculator

There are thousands of websites where people may find BMI calculators. Some are basic ones, where only height and weight are measured while in others, people need to confirm their sex, activity level and age. Generally, we advise to make use of these calculators so that you do not need to waste time calculating the BMI on your own. Of course, BMI indicator should give a rough idea regarding the health condition and weight category, however should not be the only tool for checking it. There are also groups of people who should not use BMI calculators – they are athletes, muscle builders, young children, and pregnant or breastfeeding women.

Sources:

“About Adult BMI.” Centers for Disease Control and Prevention, Centers for Disease Control and Prevention, 30 June 2020, www.cdc.gov/healthyweight/assessing/bmi/adult_bmi/index.html.

“BMI Calculator: Find out If You’re a Healthy Body Weight.” Heart Foundation NZ, www.heartfoundation.org.nz/wellbeing/bmi-calculator.

“Obesity: What Is BMI in Adults, Children, and Teens.” Medical News Today, MediLexicon International, www.medicalnewstoday.com/articles/323622.

“Why Use BMI?” Obesity Prevention Source, 13 Apr. 2016, www.hsph.harvard.edu/obesity-prevention-source/obesity-definition/obesity-definition-full-story/.