The Body Mass Index (BMI) Calculator can determine the BMI value and accompanying weight status while considering age. Use the "Metric Units" tab for the International System of Units or the "Other Units" tab to convert units to US or metric units. It should be noted that the calculator calculates both the Ponderal Index and the BMI, which are addressed in depth below.
BMI measures a person's leanness or corpulence based on height and weight and is designed to assess tissue mass. It is commonly used to indicate whether a person's body weight is appropriate for their height. Specifically, the result derived from the BMI calculation determines whether a person is underweight, normal weight, overweight, or obese, depending on which category the value falls into. These BMI values vary depending on geography and age and are sometimes further classified as severely underweight or very severely obese. Being overweight or underweight can have serious health consequences; therefore, while BMI is an inaccurate measure of healthy body weight, it can help determine whether further testing or action is necessary. The table below shows the different BMI categories used by the calculator.
The World Health Organization (WHO) recommends an adult's body weight based on BMI readings. It is suitable for both men and women aged 20 and up.
Classification BMI range - kg/m 2
Severe Thinness: < 16
Moderate Thinness (16-17) Mild. Thinness 17 - 18.5 Normal range: 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 graph depicts BMI classifications based on World Health Organization statistics. The dashed lines reflect subcategories of a major classification.
BMI Table for Children and Teens, Ages 2-20
The Centers for Disease Control and Prevention (CDC) recommends BMI categorization for children and adolescents aged 2 to 20.
Category: Percentile Range
Underweight: <5%.
Healthy weight range: 5%-85%.
Overweight risk ranges between 85% and 95%.
Overweight: >95%.
BMI chart for children and teens aged 2 to 20.
The CDC's BMI-for-age percentile growth charts.
Risks of Being Overweight
Being overweight raises the risk of a variety of major diseases and health problems. According to the Centers for Disease Control and Prevention (CDC), the following dangers exist:
High Blood Pressure
High amounts of LDL cholesterol, usually regarded as "bad cholesterol," lower HDL cholesterol levels, considered healthy cholesterol in moderation, and high levels of triglycerides.
Type 2 diabetes
Coronary Heart Disease
Stroke
Gallbladder Disease
Osteoarthritis is a joint condition caused by the destruction of joint cartilage.
Sleep apnea and breathing issues.
Specific malignancies (endometrial, breast, colon, kidney, gallbladder, liver)
Low quality of life.
Mental disorders like clinical depression, anxiety, and others
Body discomfort and trouble performing specific physical duties
In general, they have a higher risk of mortality than those with a healthy BMI.
As can be seen from the list above, being overweight can lead to a variety of bad and sometimes fatal results. In general, a person should attempt to keep their BMI below 25 kg/m2, but they should also visit their doctor to see if they need to make any lifestyle adjustments to improve their health.
Being underweight has its related hazards, as noted below:
Malnutrition, vitamin deficiencies, anemia (decreased ability to transport blood vessels)
Osteoporosis is a disease that causes bone weakening and increases the chance of fracturing a bone.
A reduction in immunological function
Growth and development concerns, notably among children and teenagers
Female reproductive difficulties may arise as a result of hormonal abnormalities that disturb the menstrual cycle. Underweight women are also more likely to miscarry in the first trimester.
Potential complications from surgery
In general, they have a higher risk of mortality than those with a healthy BMI.
In other circumstances, being underweight may indicate an underlying ailment or disease, such as anorexia nervosa, which carries its own set of hazards. Consult your doctor if you suspect you or someone you know is underweight, especially if the reason is unclear.
Although BMI is a popular and effective predictor of healthy body weight, it does have some limits. BMI is merely an estimate and does not take body composition into account. Due to the broad range of body types and the distribution of muscle, bone mass, and fat, BMI should be used with other metrics rather than as a single tool for establishing a person's healthy body weight.
BMI is incorrect because it measures extra body weight rather than excess body fat. BMI is also determined by age, gender, ethnicity, muscle mass, body fat, and activity level, among other things. For example, an elderly person who is deemed a healthy weight but is entirely passive in their everyday life may have considerable quantities of excess body fat despite not being overweight. This would be considered unhealthy, whereas a younger person with a higher muscle composition and the same BMI would be deemed healthy. Athletes, particularly bodybuilders, who are considered overweight because muscle weighs more than fat, are at a healthy weight for their body type. Generally, according to the CDC:
Older persons typically have greater body fat than younger adults with the same BMI.
Women typically have greater body fat than men with an identical BMI.
Muscular people and highly trained athletes may have higher BMIs due to increased muscle mass.
Children and adolescents:
The same criteria restricting BMI's effectiveness in adults also apply to children and adolescents. Height and sexual maturation can also influence children's BMI and body fat. BMI is a better predictor of excess body fat in obese children than in overweight children, whose BMI could be due to increased fat or fat-free mass (all body components except fat, which includes water, organs, muscle, and so on). In slim children, the variation in BMI may also be related to fat-free mass.
That being said, BMI is a good predictor of body fat for 90-95% of the population and can be used with other measurements to estimate an individual's healthy weight.
The following equations are used to calculate BMI in the International System of Units (SI) and the US Customary System (USC), using a 5'10", 160-pound individual as an example:
USC Units:
BMI is calculated as 703 x mass (lbs).
Height2 (in) = 703 × 160 702 = 22.96 kg/m2 SI Metric units:
BMI = mass (kg)
Height2 (m) = 72.57 × 1.782 = 22.90 kg/m2.
BMI BMI prime refers to a person's measured BMI compared to the "normal" upper range set by authorities like WHO and CDC. Though it may vary in some nations, such as Asia, the upper limit, BMI upper, is 25 kg/m2.
The BMI prime formula is:
BMI prime equals BMI x 25.
Because BMI prime is a ratio of two BMI values, it has no dimensions. A person with a BMI prime of less than 0.74 is considered underweight; 0.74 to 1 is considered normal; greater than 1 is considered overweight; and greater than 1.2 is considered obese. The following table displays a person's weight classification depending on their BMI prime:
Classification: BMI Prime.
Severe Thinness: <16 < 0.64.
Moderate thinness.16 - 17 0.64 - 0.68
Mild Thinness17 - 18.5 0.68 - 0.74
Normal 18.5 - 25 0.74 - 1
Overweight 25 - 30 Obese Class I: 1 - 1.2 (range 30 - 35)1.2-1.4 Obese Class II (35-40)1.4 - 1.6 Obese Class III (>40) >1.6
BMI prime allows us to quickly determine how much a person's BMI deviates from the highest limit of BMI deemed normal. It also enables comparisons between groups of people with varying top BMI limitations.
The Ponderal Index (PI) is similar to BMI in that it assesses a person's leanness or corpulence based on height and weight. The key difference between the PI and BMI is that the height is cubed rather than squared in the formula (seen below). While BMI can be useful when analyzing large groups, it is unreliable for evaluating leanness or corpulence in individuals. Although the PI and BMI have comparable concerns, the PI is more reliable for use with very tall or short persons. In contrast, BMI tends to report unusually high or low body fat levels for those at the extremes of the height and weight continuum. The equation for computing an individual's PI via USC is provided below, using a 5'10", 160-pound individual as an example:
USC Units:
PI = height (in) / mass (lbs) = 70 / 160 = 12.89 inches/pounds.
SI or Metric Units:
PI = mass (kg) x height3 (m) = 72.57 x 1.783 = 12.87 kg/m3..