BMI Calculator

The Body Mass Index (BMI) Calculator can be used to calculate BMI value and corresponding weight status while taking age into consideration. Use the "Metric Units" tab for the International System of Units or the "Other Units" tab to convert units into either US or metric units. Note that the calculator also computes the Ponderal Index in addition to BMIboth of which are discussed below in detail.

BMI introduction

BMI is a measurement of a person's leanness or corpulence based on their height and weightand is intended to quantify tissue mass. It is widely used as a general indicator of whether a person has a healthy body weight for their height. Specificallythe value obtained from the calculation of BMI is used to categorize whether a person is underweightnormal weightoverweightor obese depending on what range the value falls between. These ranges of BMI vary based on factors such as region and ageand are sometimes further divided into subcategories such as severely underweight or very severely obese. Being overweight or underweight can have significant health effectsso while BMI is an imperfect measure of healthy body weightit is a useful indicator of whether any additional testing or action is required. Refer to the table below to see the different categories based on BMI that are used by the calculator.

BMI table for adults

This is the World Health Organization's (WHO) recommended body weight based on BMI values for adults. It is used for both men and womenage 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

BMI chart for adults

This is a graph of BMI categories based on the World Health Organization data. The colors represent the major BMI categoriesand the gray contour lines represent integer BMI values for different height–weight combinations.

BMI table for children and teensage 2-20

The Centers for Disease Control and Prevention (CDC) recommends BMI categorization for children and teens between age 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 teensage 2-20

The Centers for Disease Control and Prevention (CDC) BMI-for-age percentiles growth charts.

Chart for boys
Chart for girls

Risks associated with being overweight

Being overweight increases the risk of a number of serious diseases and health conditions. Below is a list of said risksaccording to the Centers for Disease Control and Prevention (CDC):

• High blood pressure
• Higher levels of LDL cholesterolwhich is widely considered "bad cholesterol," lower levels of HDL cholesterolconsidered to be good cholesterol in moderationand high levels of triglycerides
• Type II diabetes
• Coronary heart disease
• Stroke
• Gallbladder disease
• Osteoarthritisa type of joint disease caused by breakdown of joint cartilage
• Sleep apnea and breathing problems
• Certain cancers (endometrialbreastcolonkidneygallbladderliver)
• Low quality of life
• Mental illnesses such as clinical depressionanxietyand others
• Body pains and difficulty with certain physical functions
• Generallyan increased risk of mortality compared to those with a healthy BMI

As can be seen from the list abovethere are numerous negativein some cases fataloutcomes that may result from being overweight. Generallya person should try to maintain a BMI below 25 kg/m²but ideally should consult their doctor to determine whether or not they need to make any changes to their life in order to be healthier.

Risks associated with being underweight

Being underweight has its own associated riskslisted below:

• Malnutritionvitamin deficienciesanemia (lowered ability to carry blood vessels)
• Osteoporosisa disease that causes bone weaknessincreasing the risk of breaking a bone
• A decrease in immune function
• Growth and development issuesparticularly in children and teenagers
• Possible reproductive issues for women due to hormonal imbalances that can disrupt the menstrual cycle. Underweight women also have a higher chance of miscarriage in the first trimester
• Potential complications as a result of surgery
• Generallyan increased risk of mortality compared to those with a healthy BMI

In some casesbeing underweight can be a sign of some underlying condition or disease such as anorexia nervosawhich has its own risks. Consult your doctor if you think you or someone you know is underweightparticularly if the reason for being underweight does not seem obvious.

Limitations of BMI

Although BMI is a widely used and useful indicator of healthy body weightit does have its limitations. BMI is only an estimate that cannot take body composition into account. Due to a wide variety of body types as well as distribution of musclebone massand fatBMI should be considered along with other measurements rather than being used as the sole method for determining a person's healthy body weight.

In adults:

BMI cannot be fully accurate because it is a measure of excess body weightrather than excess body fat. BMI is further influenced by factors such as agesexethnicitymuscle massbody fatand activity levelamong others. For examplean older person who is considered a healthy weightbut is completely inactive in their daily life may have significant amounts of excess body fat even though they are not heavy. This would be considered unhealthywhile a younger person with higher muscle composition of the same BMI would be considered healthy. In athletesparticularly bodybuilders who would be considered overweight due to muscle being heavier than fatit is entirely possible that they are actually at a healthy weight for their body composition. Generallyaccording 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 for an equivalent BMI.
• Muscular individuals and highly trained athletes may have higher BMIs due to large muscle mass.

In children and adolescents:

The same factors that limit the efficacy of BMI for adults can also apply to children and adolescents. Additionallyheight and level of sexual maturation can influence BMI and body fat among children. BMI is a better indicator of excess body fat for obese children than it is for overweight childrenwhose BMI could be a result of increased levels of either fat or fat-free mass (all body components except for fatwhich includes waterorgansmuscleetc.). In thin childrenthe difference in BMI can also be due to fat-free mass.

That being saidBMI is fairly indicative of body fat for 90-95% of the populationand can effectively be used along with other measures to help determine an individual's healthy body weight.

BMI formula

Below are the equations used for calculating 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 = 703× mass (lbs) height2 (in)  = 703× 160 702  = 23.0

SIMetric 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 BMI that is considered "normal," by institutions such as the WHO and the CDC. Though it may differ in some countriessuch as those in Asiathis upper limitwhich will be referred to as BMI_upper is 25 kg/m².

The BMI prime formula is:

BMI prime =

BMI  25

Since BMI prime is a ratio of two BMI valuesBMI prime is a dimensionless value. A person who has a BMI prime less than 0.74 is classified as underweight; from 0.74 to 1 is classified as normal; greater than 1 is classified as overweight; and greater than 1.2 is classified as obese. The table below shows a person's weight classification based on their 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 us to make a quick assessment of how much a person's BMI differs from the upper limit of BMI that is considered normal. It also allows for comparisons between groups of people who have different upper BMI limits.

Ponderal Index

The Ponderal Index (PI) is similar to BMI in that it measures the leanness or corpulence of a person based on their height and weight. The main difference between the PI and BMI is the cubing rather than squaring of the height in the formula (provided below). While BMI can be a useful tool when considering large populationsit is not reliable for determining leanness or corpulence in individuals. Although the PI suffers from similar considerationsthe PI is more reliable for use with very tall or short individualswhile BMI tends to record uncharacteristically high or low body fat levels for those on the extreme ends of the height and weight spectrum. Below is the equation for computing the PI of an individual using USCagain using a 5'10"160-pound individual as an example:

USC Units:

PI =  height (in) ∛mass (lbs)  =  70 ∛160  = 12.9

SIMetric Units:

PI =  mass (kg) height3 (m)  =  72.57 1.7783  = 12.9