NIH BMI Calculator

BMI is a helpful indicator of obesity and overweight. It’s determined by your height and weight. BMI is a measurement of body fat and a good indicator of your risk of diseases associated with excess body fat. Heart disease, high blood pressure, type 2 diabetes, gallstones, respiratory issues, and some malignancies are all linked to a high BMI.


How Do You Calculate BMI?

The BMI is a straightforward calculation based on a person’s height and weight. BMI = kg/m2, where kg represents a person’s weight in kilograms and m2 represents their height in meters squared. Overweight is defined as a BMI of 25.0 or higher, while the healthy range is 18.5 to 24.9.

BMI formula: weight (in kilograms) divided by height squared (in meters), expressed as kg/m2.

  • Formula: Weight (kg)/[height (m)]2
  • Example: weight = 60 kg and height = 1.50 m
  • Calculation: 60/ (1.50)2= 60/2.25=26.67

In the English System, it is calculated as follows: your weight (in pounds) divided by height squared (in inches) multiplied by 703.

  • Formula: [Weight (lb)/height (in)]2 x 703
  • Example: weight = 180 lb and height = 68 in
  • Calculation: [180/ (68)2] x 703= [180/4624] x 703= 27.37

BMI Range

Understanding your BMI result


Being underweight could indicate that you aren’t eating enough or that you are sick. A doctor can assist you if you are underweight.

Healthy Weight

Keep up the excellent work! Check out the food, nutrition, and fitness pages for advice on how to maintain a healthy weight.


If you’re overweight, a mix of food and exercise is the greatest method to reduce weight.

The BMI calculator will provide you with a personalized calorie allowance to assist you in safely achieving a healthy weight.


If you’re obese, the best strategy to reduce weight is to combine food and exercise, as well as, in some situations, medications. See a doctor for assistance and advice.

Black, Asian and Other Minority Ethnic Groups

Some long-term (chronic) illnesses, such as type 2 diabetes, are more common in black, Asian, and other minority ethnic groups.

Adults that have a BMI of:

  • More than 23 people are at risk.
  • 27.5 or more are considered high-risk.

Why Does Waist Size Matter?

Measuring your waist can help you determine if you have too much fat around your stomach, which can increase your risk of heart disease, type 2 diabetes, and stroke.

You can have a healthy BMI but still have too much stomach fat, putting you at risk for certain illnesses.

To determine your waist size, follow these steps:

  • Find your ribs at the bottom and your hips at the top.
  • Wrap a tape measure around your waist in the middle of this area.
  • Before taking the measurement, take a deep breath out normally.

If your waist is: regardless of your height or BMI, you should endeavor to reduce weight.

  • 94cm (37ins) or more for men
  • 80cm (31.5ins) or more for women

You’re at very high risk and should see a doctor if your waist is:

  • 102cm (40ins) or more for men
  • 88cm (34ins) or more for women

BMI of Children

The BMI calculator takes into account age, gender, height, and weight for children and young people aged 2 to 18.

Overweight children are regarded to be at higher risk for a range of health problems, as well as being more likely to be overweight as adults.

The BMI calculator determines whether a kid or adolescent is:

Weight Status BMI
Underweight 2nd centile or below
Healthy weight Between the 2nd and 91st centiles
Overweight 91st centile or above
Very overweight 98th centile or above

The BMI of a child is stated as a “centile” to demonstrate how it compares to other children who participated in national surveys. A girl in the 75th centile, for example, is heavier than 75 out of 100 other females her age.

Children should not have their waist sizes measured because it does not take their height into account.

If you’re worried about your child’s weight, see a doctor. They might be able to direct you to a local healthy lifestyle program for kids, teens, and families.

Limitations of the BMI

Your BMI can tell you if you’re overweight, but it can’t tell you how much fat you’re carrying. The BMI is unable to distinguish between excess fat, muscle, and bone. The adult BMI does not take age, gender, or muscle mass into consideration.

This implies:

  • Even though their body fat is low, exceptionally muscular individuals and athletes may be classified as “overweight” or “obese.” Adults who lose muscle as they age may fall into the “healthy weight” range despite carrying excess fat.
  • Pregnancy has an impact on a woman’s BMI. As you gain weight, your BMI will rise. When calculating your BMI, consider your pre-pregnancy weight.
  • Apart from these drawbacks, BMI is a simple and convenient method of determining someone’s weight.

Eating disorders

The BMI calculator results do not apply if you have an eating disorder. Please get medical advice from a doctor.

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