Body mass index calculator

BMI Calculator

Use this BMI Calculator to calculate your Body Mass Index from height and weight. You can use US units or metric units, see your adult BMI category, and estimate the healthy-weight range for your height. BMI is a screening measure, not a diagnosis, so the result should be interpreted together with other health information such as age, medical history, body composition, waist measurement, blood pressure, blood sugar, cholesterol, activity level, and advice from a qualified healthcare professional.

Calculate your BMI

Choose your preferred units, enter your height and weight, and press calculate. The calculator will display your BMI, adult BMI category, healthy-weight range for your height, and a short interpretation.

Height: feet

Example: 5

Height: inches

Example: 8

Weight: pounds

Enter body weight in pounds.

Height: centimeters

Enter height in centimeters.

Weight: kilograms

Enter body weight in kilograms.

Age group

Adult categories are used for adults. Children and teens require BMI percentile charts.

Your BMI result

25.1

Overweight range

Your BMI is 25.1, which is in the adult overweight range. BMI is a screening tool, so consider the result alongside other health information.

Height used5 ft 8 in

Weight used165.0 lb

Healthy BMI range18.5 to 24.9

Healthy weight range122.0–164.4 lb

BMI formula

Body Mass Index, usually written as BMI, is a calculation that compares body weight with height. The main idea is simple: weight is divided by height squared. Squaring height matters because a taller body naturally weighs more than a shorter body. BMI uses the square of height to create a height-adjusted weight index.

Metric BMI formula

\[ BMI=\frac{W_{\text{kg}}}{H_{\text{m}}^2} \]

\(BMI\) = Body Mass Index.

\(W_{\text{kg}}\) = body weight in kilograms.

\(H_{\text{m}}\) = height in meters.

\(H_{\text{m}}^2\) = height in meters squared.

US customary BMI formula

\[ BMI=\frac{703\times W_{\text{lb}}}{H_{\text{in}}^2} \]

\(W_{\text{lb}}\) = body weight in pounds.

\(H_{\text{in}}\) = total height in inches.

\(703\) = conversion factor for pounds and inches.

\(BMI\) = calculated body mass index.

The calculator performs these conversions automatically. If you use metric units, it converts centimeters into meters and applies the metric formula. If you use US units, it converts feet and inches into total inches and applies the US formula. The result is rounded to one decimal place because BMI categories are normally interpreted using values such as \(18.5\), \(25.0\), \(30.0\), \(35.0\), and \(40.0\).

How to use the BMI Calculator

This BMI Calculator is built for quick adult BMI screening. It is useful when you want to calculate BMI from height and weight, compare the result with standard adult BMI categories, and understand the healthy-weight range for a given height. It is not designed to diagnose health, body fat percentage, athletic fitness, or disease risk by itself.

Choose US or metric units. Use US units if your height is in feet and inches and your weight is in pounds. Use metric units if your height is in centimeters and your weight is in kilograms.
Enter your height carefully. Height has a large effect on BMI because it is squared in the formula. A small height-entry mistake can change the result noticeably.
Enter your weight. Use your current body weight. If your weight changes regularly, you may want to calculate a range rather than relying on a single number.
Select the age group. Adult BMI categories are intended for adults. Children and teens should use BMI-for-age percentiles rather than adult BMI cutoffs.
Click Calculate BMI. The calculator displays BMI, adult category, healthy-weight range, and an interpretation message.
Interpret the result cautiously. BMI is a screening measure. It should be considered together with body composition, waist measurement, medical history, lab results, and professional advice.

The most common mistake is using the wrong unit. For example, entering pounds in the kilogram field will create a result that is far too high. Entering centimeters in the inches field will create a result that is far too low. Another mistake is using adult categories for a child or teen. This calculator can show the mathematical BMI for any height and weight entered, but children and teens need percentile-based interpretation because normal body composition changes with age and sex during growth.

Adult BMI categories

For adults, BMI is commonly grouped into weight-status categories. These categories are screening ranges, not a complete health assessment. The calculator uses the adult ranges below to label the result. Obesity is also divided into classes because health risk may increase as BMI rises, but BMI alone does not explain the full health picture.

BMI range	Adult category	What it generally means
Below \(18.5\)	Underweight	The calculated BMI is below the adult healthy-weight range. A healthcare professional can help evaluate nutrition, medical causes, and overall health.
\(18.5\le BMI<25\)	Healthy weight	The calculated BMI is in the adult healthy-weight range. Other health measures still matter.
\(25\le BMI<30\)	Overweight	The calculated BMI is above the adult healthy-weight range. Body composition and health markers should be considered.
\(30\le BMI<35\)	Class 1 obesity	The calculated BMI is in the first adult obesity class. This may be associated with higher health risk, but individual assessment matters.
\(35\le BMI<40\)	Class 2 obesity	The calculated BMI is in the second adult obesity class. Professional guidance may be useful for health-risk assessment.
\(BMI\ge40\)	Class 3 obesity	The calculated BMI is in the severe obesity range. A full medical evaluation may be important for individualized care.

These ranges are convenient because they make BMI easy to interpret, but they are not perfect. Two people with the same BMI can have very different body compositions, activity levels, metabolic markers, waist measurements, and health histories. A muscular athlete may have a high BMI because muscle adds weight, while another person with the same BMI may have a different body-fat distribution and different health risks. BMI should therefore be treated as a first screen, not the final answer.

Healthy weight range formula

The calculator also estimates the adult healthy-weight range for your height. This is based on the BMI range from \(18.5\) to \(24.9\). Since BMI is calculated from weight and height, the formula can be rearranged to solve for weight when BMI and height are known.

Metric healthy weight range

\[ W_{\text{kg}}=BMI\times H_{\text{m}}^2 \]

For the lower end of the healthy-weight range, use \(BMI=18.5\). For the upper end, use \(BMI=24.9\):

\[ W_{\text{min}}=18.5\times H_{\text{m}}^2,\qquad W_{\text{max}}=24.9\times H_{\text{m}}^2 \]

US healthy weight range

\[ W_{\text{lb}}=\frac{BMI\times H_{\text{in}}^2}{703} \]

For US units, the healthy-weight range is:

\[ W_{\text{min}}=\frac{18.5\times H_{\text{in}}^2}{703},\qquad W_{\text{max}}=\frac{24.9\times H_{\text{in}}^2}{703} \]

This range is not a personal weight prescription. It is a mathematical range based on adult BMI categories. A person’s healthy weight may depend on muscle mass, frame size, body-fat distribution, ethnicity, health conditions, pregnancy status, medications, and clinical goals. Use the range as a reference point, not as a strict target.

Worked BMI examples

Worked examples help show exactly how the calculator reaches a BMI result. The formula is short, but the unit conversion matters. Below are examples using both metric and US units.

Example 1: Metric BMI calculation

Suppose a person weighs \(70\text{ kg}\) and is \(1.75\text{ m}\) tall. Substitute the values into the metric formula:

\[ BMI=\frac{70}{1.75^2} \]

\[ BMI=\frac{70}{3.0625}\approx22.9 \]

A BMI of \(22.9\) is in the adult healthy-weight range. This does not automatically prove that the person has perfect health, but it indicates that their height-adjusted weight falls within the standard adult healthy BMI category.

Example 2: US BMI calculation

Suppose a person weighs \(165\text{ lb}\) and is \(5\) feet \(8\) inches tall. First convert height into total inches:

\[ H_{\text{in}}=5\times12+8=68 \]

Then apply the US formula:

\[ BMI=\frac{703\times165}{68^2} \]

\[ BMI=\frac{115995}{4624}\approx25.1 \]

A BMI of \(25.1\) is just inside the adult overweight range. Because the value is near the boundary, the person should interpret it carefully. Hydration, scale variation, clothing, muscle mass, and measurement differences can shift the result slightly.

Example 3: Healthy-weight range for a height

For a person who is \(1.70\text{ m}\) tall, the adult healthy-weight range can be estimated as:

\[ W_{\text{min}}=18.5\times1.70^2=18.5\times2.89\approx53.5\text{ kg} \]

\[ W_{\text{max}}=24.9\times1.70^2=24.9\times2.89\approx72.0\text{ kg} \]

So, using the adult BMI category range only, a height of \(1.70\text{ m}\) corresponds to an approximate healthy-weight range of \(53.5\) to \(72.0\) kilograms. Again, this is a category-based reference, not individualized medical advice.

What your BMI result means

Your BMI result is a height-adjusted weight number. It can help identify whether your weight is below, within, or above standard adult BMI categories. It is useful because it is quick, inexpensive, and easy to calculate. It is widely used in population health, clinical screening, and educational settings. However, it should not be used alone to judge someone’s health, fitness, body composition, or worth.

If BMI is below 18.5

A BMI below \(18.5\) is categorized as underweight for adults. Possible reasons may include naturally lower body weight, nutrition issues, medical conditions, high activity demands, or recent weight loss. A healthcare professional can help evaluate the context.

If BMI is 18.5 to 24.9

This is the adult healthy-weight range. It is still possible to have health risks within this range, so other indicators such as waist measurement, blood pressure, activity level, and lab results still matter.

If BMI is 25 to 29.9

This is the adult overweight range. It may suggest higher weight for height, but it does not show whether the extra weight is muscle, fat, water, or another factor.

If BMI is 30 or higher

This is the adult obesity range and is divided into classes. Higher BMI may be associated with higher health risk, but individual evaluation is important.

One helpful way to use BMI is as a conversation starter. If your BMI is outside the range you expected, you can review your measurements, look at trends over time, and decide whether to discuss the result with a healthcare professional. A single BMI reading is less informative than a pattern combined with other health indicators.

BMI limitations

BMI is useful, but it has important limitations. It does not directly measure body fat. It does not distinguish muscle from fat. It does not show fat distribution. It does not account for pregnancy. It does not fully account for differences in body frame, ethnicity, age-related body composition, athletic training, or individual health history. These limitations are why BMI should be treated as a screening tool rather than a complete health assessment.

Muscle mass: A highly muscular person may have a high BMI even if body fat is low.
Body-fat distribution: BMI does not show whether fat is concentrated around the waist, hips, or elsewhere.
Age: Older adults may lose muscle mass, so BMI may not fully show body composition changes.
Children and teens: Adult BMI categories should not be used for children and teens because growth patterns vary by age and sex.
Pregnancy: BMI during pregnancy requires specialized interpretation and should be discussed with a healthcare professional.
Health markers: Blood pressure, cholesterol, blood sugar, fitness, diet, sleep, and medical history can all change the meaning of a BMI result.

A practical interpretation is this: BMI can flag a possible issue, but it cannot explain the issue by itself. If BMI is high, it does not automatically mean a person is unhealthy. If BMI is normal, it does not automatically mean a person is healthy. The result should be combined with other measures and professional judgment when health decisions are involved.

BMI for children and teens

This calculator includes an age-group selector because adult BMI categories should not be applied to children and teens in the same way. For people ages \(2\) to \(19\), BMI is interpreted using BMI-for-age percentiles. That means the BMI number is compared with children of the same age and sex. A child’s body composition changes as they grow, so a fixed adult cutoff such as \(25\) or \(30\) is not enough.

The formula can still calculate BMI mathematically:

\[ BMI=\frac{W_{\text{kg}}}{H_{\text{m}}^2} \]

But the interpretation should be percentile-based. For children and teens, a BMI value by itself does not tell the full category. You need age, sex, and a recognized BMI-for-age chart or calculator. This is why the result message changes when you select the child or teen age group. The calculator can still show the BMI number, but it does not assign the adult category as a final interpretation.

BMI, waist measurement, and body composition

BMI is one measure. Waist circumference, waist-to-height ratio, body-fat percentage, and medical markers can add more context. Waist measurement may be useful because abdominal fat can be connected with metabolic risk. Body-fat percentage may be useful because it separates lean mass from fat mass. Blood pressure, blood sugar, cholesterol, triglycerides, sleep, activity level, and family history can also help explain overall health risk.

Measure	What it tells you	What it does not tell you
BMI	Height-adjusted weight category.	Does not directly measure fat, muscle, or fat distribution.
Waist circumference	Approximate central body size and abdominal weight distribution.	Does not measure total body composition by itself.
Body-fat percentage	Estimated percentage of body weight from fat mass.	Accuracy depends strongly on measurement method.
Blood pressure and lab markers	Clinical health indicators related to cardiovascular and metabolic risk.	Do not directly show body size or body composition.

For many people, the best approach is to look at several measures together. If BMI is high but waist measurement, blood pressure, blood sugar, fitness, and body composition are favorable, the interpretation may be different from a person with the same BMI and several elevated risk markers. If BMI is normal but waist measurement or lab results are concerning, health risk may still need attention.

Common BMI calculator mistakes

Using the wrong unit

Make sure pounds go in the pounds field and kilograms go in the kilograms field. Unit mistakes can create extreme BMI results that are not meaningful.

Entering height incorrectly

In US units, enter feet and inches separately. A person who is \(5\) feet \(10\) inches should enter \(5\) and \(10\), not \(5.10\) feet.

Using adult cutoffs for children

Children and teens need BMI-for-age percentile interpretation. Adult ranges are for adults, not growing children.

Assuming BMI is a diagnosis

BMI is a screening number. It cannot diagnose health, body fat, disease risk, nutrition status, or fitness by itself.

Another common mistake is overreacting to a value near a boundary. For example, a BMI of \(24.9\) and a BMI of \(25.0\) are extremely close mathematically, even though they fall on different sides of a category line. Categories help with screening, but the numbers exist on a continuous scale. Small changes in measurement can move a person across a boundary.

How to use BMI responsibly

The most responsible way to use BMI is to treat it as one piece of information. If BMI is within the healthy-weight range, continue looking at overall health habits, not only weight. If BMI is outside the healthy-weight range, consider whether the result fits with your body composition, health markers, lifestyle, and medical history. If you are concerned, speak with a healthcare professional rather than making extreme changes based only on a calculator result.

Use trends: A BMI trend over time is often more useful than one measurement.
Check measurement accuracy: Use reliable height and weight measurements before interpreting the result.
Consider body composition: Muscle mass and fat distribution can change what BMI means.
Include health markers: Blood pressure, glucose, cholesterol, and other markers provide clinical context.
Avoid stigma: BMI categories should be discussed respectfully and should never be used to shame someone.
Get professional guidance: If BMI is very low, very high, changing quickly, or connected with symptoms, professional support is important.

BMI can be a useful starting point for education and planning. It can help people ask better questions: Is my weight changing? Is my BMI outside the adult reference range? Should I check my waist measurement? Should I talk to a clinician? Should I review my nutrition, strength training, sleep, stress, or activity habits? The calculator provides the number, but wise interpretation depends on context.

BMI Calculator FAQ

What is a BMI Calculator?

A BMI Calculator is a tool that calculates Body Mass Index from height and weight. It uses the formula \(BMI=\frac{W_{\text{kg}}}{H_{\text{m}}^2}\) for metric units or \(BMI=\frac{703\times W_{\text{lb}}}{H_{\text{in}}^2}\) for US units.

What is the BMI formula?

The metric BMI formula is \(BMI=\frac{W_{\text{kg}}}{H_{\text{m}}^2}\). The US formula is \(BMI=\frac{703\times W_{\text{lb}}}{H_{\text{in}}^2}\).

What is a healthy BMI for adults?

For adults, a BMI from \(18.5\) to less than \(25\) is commonly categorized as the healthy-weight range.

What BMI is considered overweight?

For adults, a BMI from \(25\) to less than \(30\) is commonly categorized as overweight.

What BMI is considered obesity?

For adults, a BMI of \(30\) or greater is commonly categorized as obesity. Obesity is also divided into Class 1, Class 2, and Class 3 ranges.

Is BMI accurate for athletes?

BMI may be less informative for athletes or people with high muscle mass because it does not distinguish muscle from fat. A muscular person may have a high BMI without having high body fat.

Can BMI diagnose health problems?

No. BMI is a screening measure, not a diagnosis. It should be interpreted with other health information and professional medical guidance when needed.

Can children use this BMI Calculator?

The calculator can calculate a BMI number, but children and teens ages \(2\) to \(19\) should be interpreted using BMI-for-age percentiles rather than adult BMI categories.

Summary

The BMI Calculator helps you calculate Body Mass Index from height and weight using either metric or US units. The metric formula is \(BMI=\frac{W_{\text{kg}}}{H_{\text{m}}^2}\), and the US formula is \(BMI=\frac{703\times W_{\text{lb}}}{H_{\text{in}}^2}\). For adults, BMI is commonly categorized as underweight, healthy weight, overweight, or obesity. The calculator also estimates a healthy-weight range for your height by rearranging the BMI formula.

The main lesson is that BMI is useful but limited. It is quick, easy, and widely used, but it does not directly measure body fat, muscle mass, fat distribution, or overall health. Use BMI as a screening number and combine it with other information when making health decisions. If your result is concerning, unexpected, very low, very high, or connected with symptoms, consider speaking with a qualified healthcare professional.

BMI Calculator | Body Mass Index Formula & Category

BMI Calculator

Calculate your BMI