BMI Calculator

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Enter your measurements and press Calculate BMI.

The Body Mass Index (BMI) Calculator is a tool used to estimate BMI and determine the corresponding weight category, while also taking age into account. You can use the “Metric Units” tab for the International System of Units or the “Other Units” tab to convert values into US or metric units. The calculator also provides the Ponderal Index alongside BMI, and both are explained in more detail below.

What BMI Is

BMI is a way of measuring whether a person is lean or overweight based on their height and weight. It is meant to give a general idea of body tissue mass. It is commonly used as a simple indicator of whether someone has a healthy body weight for their height. More specifically, the BMI value is used to place a person into categories such as underweight, normal weight, overweight, or obese, depending on which range the value falls into. These BMI ranges can differ by region and age, and are sometimes split into more specific groups such as severe underweight or very severely obese. Since being overweight or underweight can have serious health consequences, BMI is not a perfect measure of healthy weight, but it can still be a helpful sign of whether further testing or action may be needed. The table below shows the categories used by the calculator.

BMI Table for Adults

This table is based on the World Health Organization’s (WHO) recommended body weight categories according to BMI for adults. It applies to both men and women aged 20 or older.

Classification BMI range – kg/m²

Severe Thinness 16

Moderate Thinness 16 – 17

Mild Thinness 17 – 18.5

Normal 18.5 – 25

Overweight 25 – 30

Obese Class I 30 – 35

Obese Class II 35 – 40

Obese Class III 40

Classification	BMI range – kg/m²
Severe Thinness	16
Moderate Thinness	16 – 17
Mild Thinness	17 – 18.5
Normal	18.5 – 25
Overweight	25 – 30
Obese Class I	30 – 35
Obese Class II	35 – 40
Obese Class III	40

BMI Chart for Adults

This is a graph of BMI categories based on WHO data. The colors show the main BMI categories, while the gray contour lines represent whole-number BMI values for different height and weight combinations.

BMI Table for Children and Teens, Age 2–20

The Centers for Disease Control and Prevention (CDC) recommends the following BMI categories for children and teens between the ages of 2 and 20.

Category Percentile Range

Underweight < 5%

Healthy weight 5% – 85%

At risk of overweight 85% – 95%

Overweight > 95%

BMI Chart for Children and Teens, Age 2–20

These are the CDC BMI-for-age percentile growth charts.

Chart for boys

Chart for girls

Risks of Being Overweight
Being overweight raises the risk of several serious diseases and health conditions. According to the CDC, these risks include:
High blood pressure
Higher levels of LDL cholesterol, often called “bad cholesterol,” lower levels of HDL cholesterol, which is considered good cholesterol in moderation, and high triglyceride levels
Type II diabetes
Coronary heart disease
Stroke
Gallbladder disease
Osteoarthritis, a joint disease caused by the breakdown of joint cartilage
Sleep apnea and breathing problems
Certain cancers, including endometrial, breast, colon, kidney, gallbladder, and liver cancer
Lower quality of life
Mental health conditions such as clinical depression, anxiety, and others
Body pain and difficulty with certain physical activities
Generally, a higher risk of death compared with people who have a healthy BMI

As this list shows, being overweight can lead to many negative outcomes, some of which can be fatal. In general, a person should aim to keep their BMI below 25 kg/m², but it is best to talk to a doctor to decide whether any lifestyle changes are needed for better health.

Risks of Being Underweight

Being underweight also comes with its own risks, including:

Malnutrition, vitamin deficiencies, and anemia, which reduces the ability to carry blood vessels
Osteoporosis, a disease that weakens bones and increases the risk of fractures
A weaker immune system
Growth and development problems, especially in children and teenagers
Possible reproductive problems in women due to hormonal imbalances that can interfere with the menstrual cycle. Underweight women also have a higher risk of miscarriage in the first trimester
Possible complications after surgery
Generally, a higher risk of death compared with people who have a healthy BMI

In some cases, being underweight may be a sign of an underlying condition or disease, such as anorexia nervosa, which carries its own risks. If you think you or someone you know is underweight, especially if the reason is not clear, it is important to consult a doctor.

Limitations of BMI

Although BMI is widely used and useful for indicating healthy body weight, it has limitations. BMI is only an estimate and cannot account for body composition. Because body types vary greatly, and because muscle, bone mass, and fat are distributed differently in different people, BMI should be used together with other measurements rather than as the only way to judge a person’s healthy body weight.

In adults:

BMI cannot be completely accurate because it measures excess body weight, not excess body fat. BMI is also affected by factors such as age, sex, ethnicity, muscle mass, body fat, and activity level, among others. For example, an older person who is considered a healthy weight but is completely inactive may have a significant amount of excess body fat even if they are not heavy. This would be unhealthy, while a younger person with more muscle and the same BMI would be considered healthy. In athletes, especially bodybuilders who may be classified as overweight because muscle is heavier than fat, it is entirely possible that they are actually at a healthy weight for their body composition. According to the CDC:

Older adults tend to have more body fat than younger adults with the same BMI.
Women tend to have more body fat than men with the same BMI.
Muscular people and highly trained athletes may have higher BMIs because of large muscle mass.

In children and adolescents:

The same factors that limit BMI’s usefulness in adults can also apply to children and adolescents. In addition, height and sexual maturation can affect BMI and body fat in children. BMI is a better indicator of excess body fat in obese children than in overweight children, whose BMI may be caused by higher levels of either fat or fat-free mass, which includes water, organs, muscle, and other body components except fat. In thin children, differences in BMI can also be due to fat-free mass. That said, BMI is a fairly good indicator of body fat for 90–95% of the population, and it can be used effectively along with other measures to help determine a person’s healthy body weight.

BMI Formula

Below are the equations used to calculate BMI in the International System of Units (SI) and the US customary system (USC), using a 5'10", 160-pound person as an example.

USC Units:

BMI = 703 × mass (lbs) / height² (in)

= 703 × 160 / 70²

= 23.0

SI, Metric Units:

BMI = mass (kg) / height² (m)

= 72.57 / 1.778²

= 23.0

BMI Prime

BMI prime is the ratio of a person’s measured BMI to the upper limit of what is considered “normal” BMI by institutions such as the WHO and the CDC. Although this limit may differ in some countries, such as those in Asia, the upper limit used here, called BMIupper, is 25 kg/m².

The BMI prime formula is:

BMI prime = BMI / 25

Because BMI prime is a ratio of two BMI values, it has no units. A person with a BMI prime below 0.74 is classified as underweight; from 0.74 to 1 is normal; above 1 is overweight; and above 1.2 is obese. The table below shows weight classification based on BMI prime.

Classification BMI BMI Prime

Severe Thinness < 16 < 0.64

Moderate Thinness 16 – 17 0.64 – 0.68

Mild Thinness 17 – 18.5 0.68 – 0.74

Normal 18.5 – 25 0.74 – 1

Overweight 25 – 30 1 – 1.2

Obese Class I 30 – 35 1.2 – 1.4

Obese Class II 35 – 40 1.4 – 1.6

Obese Class III > 40 > 1.6

BMI prime allows a quick assessment of how much a person’s BMI differs from the upper limit of normal BMI. It also makes it possible to compare groups of people who have different upper BMI limits.

Ponderal Index

The Ponderal Index (PI) is similar to BMI because it also measures how lean or overweight a person is based on height and weight. The main difference between PI and BMI is that PI cubes the height instead of squaring it, as shown in the formula below. While BMI can be useful when looking at large populations, it is not reliable for determining leanness or corpulence in individuals. Although PI has similar issues, it is more reliable for very tall or very short people, while BMI tends to give unusually high or low body fat levels for those at the extremes of height and weight.

Below is the equation for calculating PI using USC, again using a 5'10", 160-pound person as an example.

USC Units:

PI = height (in) / ∛mass (lbs)

= 70 / ∛160

= 12.9