BMI Calculator

Modify the values and click the Calculate button to use

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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 BMI, both of which are discussed below in detail.

BMI Introduction

BMI (Body Mass Index) is a measurement that evaluates a person’s leanness or fatness based on their height and weight. It is designed to estimate tissue mass and serves as a general indicator of whether an individual has a healthy body weight in relation to their height. The BMI value derived from this calculation helps classify individuals into categories such as underweight, normal weight, overweight, or obese, depending on which range the value falls within. These BMI ranges may vary depending on factors like age and region, and are sometimes further subdivided into classifications such as severely underweight or very severely obese. Since being either underweight or overweight can have serious health implications, BMI—despite being an imperfect tool—is a helpful screening measure to determine whether further assessment or action is necessary. Refer to the table below for the different BMI categories used by the calculator.

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BMI Table for Adults

This table represents the World Health Organization’s (WHO) recommended body weight classifications based on BMI values for adults. It applies to both men and women aged 20 and above.

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 Table for Children and Teens (Ages 2–20)

The Centers for Disease Control and Prevention (CDC) provides BMI categorization for children and teens aged 2 to 20 years.

Category	Percentile Range
Underweight	< 5%
Healthy Weight	5% – 85%
At Risk of Overweight	85% – 95%
Overweight	> 95%

BMI-for-Age Percentile Chart – Boys (2–20 Years)

Age (Years)	5th %ile	10th %ile	25th %ile	50th %ile	75th %ile	85th %ile	95th %ile
2	14.4	14.8	15.6	16.5	17.5	18.2	19.4
5	13.8	14.2	15.1	15.9	16.8	17.5	18.9
10	14.2	14.7	15.9	17.0	18.4	19.3	21.1
15	17.4	18.1	19.5	21.2	23.2	24.3	26.8
20	18.7	19.5	21.0	22.7	24.6	25.7	28.3

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📊 BMI-for-Age Percentile Chart – Girls (2–20 Years)

Age (Years)	5th %ile	10th %ile	25th %ile	50th %ile	75th %ile	85th %ile	95th %ile
2	14.2	14.5	15.3	16.3	17.3	18.0	19.3
5	13.6	14.0	14.9	15.8	16.8	17.5	18.9
10	14.2	14.8	16.1	17.4	19.1	20.2	22.3
15	17.6	18.3	20.0	21.8	23.7	25.0	27.6
20	18.8	19.5	21.2	22.9	24.7	25.9	28.3

Risks Associated with Being Overweight

Being overweight raises the likelihood of developing numerous serious health conditions. According to the CDC, these risks include:

• High blood pressure
• Elevated LDL (“bad”) cholesterol and triglycerides; reduced HDL (“good”) cholesterol
• Type II diabetes
• Coronary heart disease
• Stroke
• Gallbladder disease
• Osteoarthritis (joint damage due to cartilage breakdown)
• Sleep apnea and respiratory issues
• Certain cancers (e.g., endometrial, breast, colon, kidney, gallbladder, liver)
• Lower quality of life
• Mental health disorders (e.g., depression, anxiety)
• Physical discomfort and functional limitations
• Increased risk of mortality compared to individuals with a healthy BMI

Maintaining a BMI below 25 kg/m² is generally recommended, but it is best to consult a healthcare provider for personalized guidance.

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Risks Associated with Being Underweight

Being underweight also presents various health risks, including:

• Malnutrition, vitamin deficiencies, anemia (reduced oxygen-carrying capacity of blood)
• Osteoporosis (weakened bones prone to fractures)
• Weakened immune system
• Impaired growth and development (especially in children and teens)
• Reproductive issues in women due to hormonal imbalances and increased miscarriage risk
• Potential complications during surgery
• Increased risk of mortality

In some cases, being underweight may indicate an underlying condition such as anorexia nervosa. It is advisable to seek medical evaluation if the cause of low body weight is unclear.

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Limitations of BMI

While BMI is a widely used indicator, it has notable limitations. It does not differentiate between muscle, fat, and bone mass. Therefore, it should not be the sole method for assessing a person’s health status.

In Adults:

BMI reflects excess weight, not necessarily excess fat. Influencing factors include:

• Age
• Sex
• Ethnicity
• Muscle mass
• Activity level

Examples:

• Older adults often have more body fat than younger individuals with the same BMI.
• Women typically have more body fat than men at the same BMI.
• Athletes may have high BMIs due to muscle mass, not fat.

In Children and Adolescents:

The same limitations apply. Additionally, height and sexual maturity affect BMI and body fat levels. BMI is more accurate for identifying obesity in children than for distinguishing between overweight and higher muscle mass.

Still, for about 90–95% of the population, BMI serves as a reliable indicator when used alongside other metrics.

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BMI Formula

Here are the formulas used to calculate BMI in both the U.S. Customary and International Systems, using a person who is 5’10” and 160 lbs as an example:

USC Units
BMI = 703 × (mass in lbs) / (height in inches)²
BMI = 703 × 160 / 70² = 23.0

SI (Metric) Units
BMI = mass in kg / (height in m)²
BMI = 72.57 / 1.778² = 23.0

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BMI Prime

BMI Prime is the ratio of a person’s BMI to the upper limit of the “normal” BMI range (commonly 25 kg/m² as per WHO and CDC).

BMI Prime Formula:
BMI Prime = BMI / 25

Because it’s a ratio, BMI Prime is dimensionless. Classification ranges:

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 quickly highlights how much a person’s BMI deviates from the upper limit of the healthy range and enables comparisons across different population standards.

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Ponderal Index (PI)

The Ponderal Index is another method to assess leanness or corpulence, differing from BMI by using cubed height in its calculation. While BMI works well for broad populations, PI is better suited for very tall or very short individuals, for whom BMI may overestimate or underestimate body fat.

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

SI (Metric) Units
PI = mass (kg) / height³ (m)
PI = 72.57 / 1.778³ = 12.9