Body Mass Index (BMI) is a measurement that uses your height and weight to determine whether your weight is healthy or not.
The BMI calculation takes an adult’s weight in kilograms and divides it by their height in meters squared. For example, A BMI of 25 means 25kg/m2. BMI tests for weight categories that may contribute to health concerns. But it does not assess an individual’s body fatness or health.
BMI = weight (kg) / height (m)²
BMI is the most widely used indicator for categorizing obesity in adults. It is also suggested for use with children and adolescents.
A Screening Tool
BMI, like weight-for-size, is a screening technique used to detect people who are underweight or overweight. The BMI scale is NOT a diagnostic instrument.
A child who is relatively heavy may have a high BMI for his or her age or a high weight-for-stature. Further evaluation, such as skinfold measures, would be required to determine whether the youngster has extra fat. Diet, health, and physical activity assessments are required to develop a counseling strategy.
For children, BMI is gender and age-dependent. BMI-for-age is the measure used for children aged 2 to 20 years because BMI fluctuates significantly with age.
Body Mass Index Ranges
The optimum BMI for most persons is between 18.5 and 24.9.
For children and adolescents aged 2 to 18, the BMI calculation considers age, gender, height, and weight.
If your BMI is:
- below 18.5 – you’re in the underweight range
- between 18.5 and 24.9 – you’re in the healthy weight range
- between 25 and 29.9 – you’re in the overweight range
- between 30 and 39.9 – you’re in the obese range
If you want to calculate your BMI, try our healthy weight calculator.
How to calculate Body Mass Index
Body Mass Index is a simple calculation using a person’s height and weight. The formula is BMI = kg/m2 where kg is a person’s weight in kilograms and m2 is their height in meters squared.
A BMI of 25.0 or more is overweight, while the healthy range is 18.5 to 24.9.
Calculating BMI
1. Using the Metric System
The formula for BMI in the metric system is weight in kilogrammes divided by height in metres squared. Because height is generally measured in centimeters, an alternative calculating formula is dividing the weight in kilogrammes by the height in centimetres squared.
It is necessary to multiply by 10,000 to convert BMI to meters since stature measurements are generally taken in centimeters. There are 100 centimeters in a meter and since stature is squared, we must convert as such: 100 x 100 = 10,000.
When using a hand calculator;
- Divide weight (kg) by height (cm) squared, multiply by 10,000, then round to one decimal point if your calculator supports a square function.
- If your calculator lacks a square function, divide the weight by the height twice as given in the calculation formula above, multiply by 10,000, then round to one decimal place.
Calculations for BMI can be completed as a continuous equation.
2. Using the English System
When using English measurements, convert ounces (oz) and fractions to decimal values. Then, multiply your weight in pounds (lbs) by your height in inches (in) squared by a conversion factor of 703.
- If your handheld calculator has a square function, divide weight (lbs) by height (in) squared, multiply by 703, and round to one decimal place.
- If your calculator lacks a square function, divide your weight by your height twice as shown in the previous calculation, multiply by 703, and round to one position of decimal.
Calculations for BMI can be completed as a continuous equation
Accuracy of Body Mass Index
BMI considers natural differences in body form to determine a healthy weight range for a given height.
In addition to evaluating your BMI, if you are a healthy weight, healthcare experts may consider other criteria.
muscle is much denser than fat, particularly muscular persons, such as heavyweight boxers, weight trainers, and sportsmen may be a healthy weight despite having an obese BMI.
Your race can also influence your risk of certain health disorders. For example, adults of South Asian heritage, having a BMI of 23, which is considered healthy, may be at a higher risk of certain health concerns, such as diabetes.
If you are pregnant, you should not use BMI as a measurement. If you’re worried about your weight, talk to your midwife or doctor.
Who shouldn’t use a BMI calculator?
BMI is not used for bodybuilders, long-distance runners, pregnant women, the elderly, or children under the age of five. This is due to the fact that BMI does not consider whether the weight is carried as muscle or fat, only the number.
For example, athletes who have a higher muscle mass may have a higher BMI but are not at increased health risk. Those with lesser muscle mass, such as children who have not finished growing or the elderly who may be losing muscle mass, may have a lower BMI. For a woman whose body composition changes throughout pregnancy and nursing, utilizing BMI is inappropriate.
BMI calculator for women
To calculate your BMI, use this adult BMI calculator.
You can also use these formulas to calculate your BMI:
- U.S. units. (Weight in pounds ÷ height2 in inches) x 703 = BMI (For example: 150 pounds ÷ 65 inches2 x 703 = 26.6)
- Metric units. Weight in kilograms ÷ height2 in meters = BMI (For example: 70 kilograms ÷ 1.7 meters2 = 24.2)
BMI ranges for women
A healthy BMI for women falls between 18.5 and 24.9. Find your BMI in the chart below to see your weight classification.
| BMI | Weight classification |
| Below 18.5 | Underweight |
| 18.5-24.9 | Normal |
| 25.0-29.9 | Overweight |
| 30.0 or higher | Obese |
If you’re pregnant or plan on becoming pregnant, you can calculate your recommended weight gain using your pre-pregnancy BMI.
| BMI before pregnancy | Recommended pregnancy weight gain |
| Below 18.5 | 28 to 40 pounds |
| 18.5-24.9 | 25 to 35 pounds |
| 25.0-29.9 | 15 to 25 pounds |
| 30.0 or higher | 11 to 20 pounds |
Is BMI Same for Adults, Teens and Children
BMI is perceived differently in children and adolescents, despite the fact that it is calculated using the same formula as adult BMI. The BMI of children and teenagers must be age and gender specific because the amount of body fat changes with age and differs between girls and boys. The CDC BMI-for-age growth charts account for these variations and visually display BMI as a percentile rating.
Obesity in children aged 2 to 19 is defined as a BMI at or above the 95th percentile among children of the same age and gender in the reference sample from 1963 to 1994.
For example, a 10-year-old kid of typical height (56 inches) and weight 102 pounds, has a BMI of 22.9 kg/m2. This would put the youngster in the 95th percentile for BMI, which means his BMI is higher than 95% of similarly aged boys in this reference sample, and he would be termed obese.
How good is BMI as an indicator of body fatness?
Although there is a high association between BMI and body fatness1,2,3,7, two people with the same BMI may have different levels of body fatness.
In general,
- At the same BMI, women tend to have more body fat than men.
- At the same BMI, the amount of body fat may be higher or lower depending on the racial/ethnic group13-15.
- At the same BMI, older people, on average, tend to have more body fat than younger adults.
- At the same BMI, athletes have less body fat than do non-athletes.
BMI appears to be more accurate as an indicator of body fatness in people with greater levels of BMI and body fatness16. While a person with a very high BMI (e.g., 35 kg/m2) is very likely to have high body fat.
A person with a reasonably high BMI can have either high body fat or high lean body mass. To assess an individual’s health state and dangers, a skilled healthcare provider should conduct appropriate health assessments.
Increase BMI is a risk of Diseases
People who have obesity are at increased risk for many diseases and health conditions, including the following:
- All-causes of death (mortality)
- High blood pressure (hypertension)
- High LDL cholesterol, low HDL cholesterol, or high levels of triglycerides (dyslipidemia)
- Type 2 diabetes
- Coronary heart disease
- Stroke
- Gallbladder disease
- Osteoarthritis (a breakdown of cartilage and bone within a joint)
- Sleep apnea and breathing problems
- Chronic inflammation and increased oxidative stress
- Some cancers (endometrial, breast, colon, kidney, gallbladder, and liver)
- Low quality of life
- Mental illness such as clinical depression, anxiety, and other mental disorders21,22
- Body pain and difficulty with physical functioning
How to lower your Body Mass Index?
Lowering your BMI as rapidly as possible isn’t always the greatest technique for long-term results. Slower weight loss and measuring other health metrics in addition to BMI can give you a higher chance of keeping the weight off and feeling happy.
1. Set the realistic goal
BMI is based on our body weight. Therefore, lowering the BMI means lowering your weight.
You should aim to lose 1 to 2 pounds per week by consuming 500 to 1,000 calories less than you expend each day. Use an internet calculator to evaluate your current calorie demands, then remove 500 to 1,000 calories to get your calorie intake target for weight loss.
If you need to lose a lot of weight, aim for a 1,000-calorie deficit; if you’re already slim, a 500-calorie deficit is probably more acceptable. To achieve your nutritional needs, consume at least 1,400 calories each day and avoid putting your body into a semi-starvation state.
When you have an idea of your desired weight range and your expected rate of weight reduction, you can create a realistic timetable for achieving your objectives.
Don’t be concerned if your projected weight loss will take months or even years; slower weight loss is more beneficial than fad dieting for quick weight loss.
2. Choose healthy food
Making wise dietary choices when losing weight not only nourishes your body with vitamins and minerals and keeps you feeling full, but it also enhance your metabolism. Protein is difficult to digest, it has a significant thermic impact. As a result, you expend more calories in your digestive tract breaking it down.
With a 30% thermic impact, you’ll burn 30 calories for every 100 calories of protein you consume. In comparison, digesting 100 calories of fat requires only 3 calories while digesting 100 calories of carbohydrates requires only 7 calories.
To figure out how much protein you need each day, multiply your weight in pounds by 0.8; for a 170-pound individual, that’s 136 grammes of protein each day. Choose skinless and boneless turkey and chicken breast, as well as tilapia, tuna, and salmon; tofu, tempeh, and nonfat soy milk; nonfat dairy and eggs; and nuts, seeds, and beans.
Fill up the remainder of your diet with nutritious whole grains, which give carbohydrates to keep you going; fruits and veggies, which are high in vitamins, minerals, and fiber; dairy, which provides calcium and protein; and healthy fats, such as olive oil and avocado.
3. Accelerate weight loss with exercise
If you want to lose weight and lower your BMI quickly, you must increase your physical activity. Aerobic activity burns calories, which allows you to establish a larger calorie deficit for weight loss without drastically reducing your food intake.
If you’re new to cardio, start with a low-impact activity that you love, such as brisk walking, the elliptical machine, or water aerobics, and gradually increase the intensity as you get fitter.
The more intense your activity, the better for weight reduction; strenuous workouts cause “afterburn,” which means you’ll have a greater metabolism for hours, or even up to two days after your workout. In order to increase your afterburn, include high-intensity intervals into your regimen as you improve your cardiovascular fitness.
Combine aerobics with full-body strength training workouts two or three times each week. Building muscle through strength training increases your calorie burn (since muscle requires more calories to maintain than fat), allowing you to lose weight more easily and keep it off longer.
4. Track your progress and Body Mass Index
Keep a record of your weight-loss progress by tracking your progress. While you may be eager to get your BMI into the “normal” range, you should also consider other health indicators. For instance, track changes in your waist size over time.
Your health improves when you burn off excess belly fat that was previously growing your waistline. Look for other signals that you’re getting healthier, such as being able to work out longer, at a higher intensity during cardio, or lifting larger weights during strength-training routines.
Don’t become obsessed with achieving a specific weight or BMI. As you lose weight, evaluate how you look and feel, not simply your weight and BMI, as the final indicator of whether you’ve met your goals.