Body mass index (BMI) calculator

Body mass index (BMI) is a measurement of a person’s body fat based on their weight and height. It is a widely used tool to assess whether a person has a healthy weight or is at risk of health problems due to excess weight. This BMI calculator allows you to calculate your BMI.

There are two BMI calculators available here: one for adults (ages 20 and older) and another for children and teenagers (ages 2 through 19). The calculators automatically compute BMIs based on default values. To perform a different BMI calculation, simply modify the relevant fields. As you change the values, the calculator will instantly update the BMI results and other text.

BMI calculator for adults (for people 20 years and older)

BMI calculator for children and teen (ages 2 through 19 years)

Related calculators:

Body type Ideal weight Healthy weight Body surface

BMI ranges for adults

The World Health Organization (WHO) provides the following BMI ranges to classify adults’ weight status:

Underweight: BMI less than 18.5
Normal weight: BMI between 18.5 and 24.9
Overweight: BMI between 25 and 29.9
Obesity Class I: BMI between 30 and 34.9
Obesity Class II: BMI between 35 and 39.9
Obesity Class III: BMI of 40 or greater

These BMI categories are used to assess an individual’s weight status and provide a general guideline for whether their weight falls within a healthy range. It’s important to note that while BMI is a useful tool for assessing weight on a population level, it has limitations and doesn’t take into account other factors such as muscle mass, body composition, and distribution of weight. Therefore, it should be used as a screening tool, and individual health assessments may require additional information and measurements. Additionally, these ranges may not be applicable to children and adolescents, as growth patterns and body composition vary during different stages of development.

BMI ranges for children and teen

The Centers for Disease Control and Prevention (CDC) in the United States provides BMI categories specifically for children and teenagers (ages 2 through 19) based on age and gender percentiles. These categories help assess how a child’s or teen’s BMI compares to others of the same age and gender. Here are the BMI categories for children and teens according to the CDC:

Underweight: Less than the 5th percentile for age and gender.
Healthy weight: Between the 5th percentile and less than the 85th percentile for age and gender.
Overweight: Between the 85th percentile and less than the 95th percentile for age and gender.
Obesity: Equal to or greater than the 95th percentile for age and gender.

These percentiles are based on growth charts developed by the CDC, which take into account the normal range of BMI values for children and teens at different ages and genders. It’s important to note that children and teens are assessed differently than adults because their bodies are still growing and developing. This approach helps healthcare professionals and parents better understand how a child’s or teen’s weight compares to their peers, considering their age and gender.

The BMI formula

BMI is calculated using a simple formula that takes into account a person’s weight and height. The BMI formula takes a person’s weight in kilograms and divides it by their height in meters squared. The formula for BMI is:

\text{BMI} = \frac{\text{weight in kilograms}}{(\text{height in meters})^2}

To calculate your BMI, you need to know your weight in kilograms and your height in meters. If you only know your weight in pounds and your height in inches, you can use the following formula to convert them to kilograms and meters:

Weight in kilograms = weight in pounds / 2.20462

Height in meters = height in inches x 0.0254

The resulting number is then compared to standard BMI ranges to determine if a person is underweight, normal weight, overweight, or obese.

If you want to use the the United States customary system (USC), the formula for calculating BMI (Body Mass Index) is as follows:

\text{BMI} = 703\times\frac{\text{weight in pounds}}{(\text{height in inches})^2}

Here’s how it works:

Measure your weight in pounds.
Measure your height in inches.
Square your height (multiply your height in inches by itself).
Divide your weight in pounds by the result from step 3.
Multiply the quotient from step 4 by 703 to get your BMI.

The result will be your BMI, which is a numerical value that represents your body mass in relation to your height. This formula is specific to the USC units of pounds for weight and inches for height.

BMI prime

BMI prime, often denoted as BMI’, is a variation of the Body Mass Index (BMI) that takes into account an individual’s BMI in relation to the normal or healthy BMI range. While the traditional BMI provides a measure of body weight relative to height, BMI prime adjusts this value to express it as a ratio compared to the upper limit of the healthy BMI range.

The formula for calculating BMI prime is as follows:

\text{BMI prime} = \frac{\text{BMI}}{\text{25}}

In this formula, 25 is considered the upper limit of the healthy BMI range. When BMI prime equals 1, it indicates that the person’s BMI falls exactly within the healthy weight range. A value less than 1 suggests that the person’s BMI is below the healthy weight range, while a value greater than 1 indicates that the person’s BMI is above the healthy weight range.

Here’s how to interpret BMI prime values:

BMI < 1: Underweight
BMI = 1: Healthy or Normal Weight
BMI > 1: Overweight or Obese

BMI prime can be a useful tool for assessing how an individual’s BMI compares to the healthy weight range and provides additional context beyond the traditional BMI measurement.

Ponderal index

The ponderal index (PI) is a measure used to assess an individual’s body composition and is an alternative to the Body Mass Index (BMI). While BMI is a commonly used measure that relates an individual’s weight to their height, the ponderal index takes into account the three dimensions of an individual’s body: height, weight, and width. It is particularly useful for evaluating body composition in growing children and adolescents.

The formula for calculating the ponderal index is as follows:

\text{Ponderal index} = \frac{\text{weight in kilograms}}{(\text{height in meters})^3}

Unlike BMI, which uses the square of height (height squared) in its denominator, the ponderal index uses the cube of height (height cubed). This adjustment takes into consideration that as an individual grows taller, their body becomes more three-dimensional.

Interpreting the ponderal index is somewhat similar to interpreting BMI:

A low ponderal index suggests that an individual may be relatively lean or underweight for their height and body dimensions.
A ponderal index within a certain range is considered normal or healthy for an individual’s height and body proportions.
A high ponderal index may indicate that an individual is overweight or has an excess of body fat for their height and body dimensions.

It’s important to note that while the ponderal index provides an alternative way to assess body composition, it is not as commonly used or well-established as BMI in clinical practice. Healthcare professionals often rely on a combination of measurements and assessments to evaluate an individual’s overall health and body composition.

Caution

It’s important to note that while BMI can be a useful tool for assessing body weight, it is not always accurate. For example, it may not take into account differences in muscle mass, bone density, or body composition between individuals. As such, it’s always a good idea to talk to a healthcare professional if you have concerns about your weight or body composition.