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BMI Calculator

Calculate adult body mass index from height and weight using metric or U.S. units. BMI is a quick screening measure that helps classify weight status, compare results with standard adult BMI categories, and discuss weight trends with a qualified healthcare professional.

Adult categories follow CDC BMI ranges. For children and teens, BMI is interpreted by age and sex percentiles.

Result

Your BMI

Adult screening

BMI score

24.2

Within the adult healthy weight range.

Category

Healthy Weight

Healthy Range

53.5-72.0 kg

Adult BMI Categories

UnderweightBelow 18.5
Healthy Weight18.5 to less than 25
Overweight25 to less than 30
Obesity30 or greater

Guide

What Is BMI?

Body mass index is a calculated measure of body weight relative to height. Healthcare professionals commonly use BMI as a quick adult screening tool because it is simple, inexpensive, and standardized across metric and U.S. units.

BMI is not a diagnosis and does not directly measure body fat. It is best used as one piece of context alongside medical history, physical exam findings, waist circumference, lab results, and body composition when those details are available.

Formula

BMI Formula

Metric formula

BMI = weight (kg) / height2 (m2)

Weight is kilograms and height is meters squared.
U.S. formula

BMI = 703 x weight (lb) / height2 (in2)

Weight is pounds and height is total inches squared.

Method

How the Calculator Works

HeightEnter centimeters in Metric mode, or feet and inches in U.S. mode.
WeightEnter kilograms in Metric mode, or pounds in U.S. mode.
CategoryThe calculator assigns the adult BMI category from the calculated BMI score.

Chart

Adult BMI Categories

BMIClassification
Below 18.5Underweight
18.5-24.9Healthy Weight
25.0-29.9Overweight
30.0-34.9Obesity Class I
35.0-39.9Obesity Class II
40 or higherObesity Class III

Adult BMI classifications may vary slightly between organizations and populations. Children and teens use age- and sex-specific BMI percentiles rather than this adult chart.

Example

Example Calculation

Example inputs: height 175 cm and weight 70 kg.

  1. Convert height to meters: 175 cm = 1.75 m.
  2. Substitute the values: BMI = 70 / (1.75 x 1.75).
  3. Square height: 1.75 x 1.75 = 3.0625.
  4. Divide weight by height squared: 70 / 3.0625 = 22.9.
Interpretation: a BMI of 22.9 is in the adult Healthy Weight category. This is a screening result, not a diagnosis of health or fitness.

Use

How to Use the BMI Calculator

  1. Select Metric or U.S. units.
  2. Enter your height in the visible height fields.
  3. Enter your weight in the visible weight field.
  4. Review the automatically updated BMI score and category.
  5. Read the healthy range, category chart, and interpretation notes.

Results

Understanding Your Results

UnderweightMay indicate body weight is below the adult reference range for height.
Healthy WeightFalls within the standard adult BMI reference range.
OverweightFalls above the standard adult healthy weight BMI range.
Obesity ClassesBMI of 30 or higher is subdivided into Class I, Class II, and Class III.

BMI does not directly measure body fat. Muscle mass, age, ethnicity, pregnancy, body composition, and waist circumference can all affect interpretation.

Practical Notes

Benefits and Limitations

BenefitsBMI is quick, easy to calculate, widely accepted, useful for adult screening, and helpful for monitoring broad weight trends over time.
LimitationsBMI may be less informative for athletes, bodybuilders, older adults, pregnant individuals, children, adolescents, and some ethnic populations.

Accuracy

Tips and Common Mistakes

Tips for Accurate Results

  • Measure height without shoes.
  • Weigh yourself under consistent conditions.
  • Select the correct unit system before entering values.
  • Double-check height and weight entries.

Common Mistakes

  • Mixing metric and U.S. units.
  • Entering inches as feet or centimeters as meters.
  • Using outdated height or weight measurements.
  • Treating BMI as a diagnosis.
  • Applying adult BMI categories to children.

FAQ

Frequently Asked Questions

What is BMI?

BMI, or body mass index, is a height-and-weight calculation used to estimate adult weight status.

How is BMI calculated?

Metric BMI is weight in kilograms divided by height in meters squared. U.S. BMI is 703 times weight in pounds divided by height in inches squared.

What is a healthy BMI for adults?

For most adults, a BMI from 18.5 to 24.9 is classified as healthy weight by CDC adult BMI categories.

Is BMI accurate?

BMI is useful as a screening tool, but it does not directly measure body fat, fitness, or overall health.

Does BMI measure body fat?

No. BMI uses height and weight only. Body fat, muscle, bone density, and fat distribution require other assessments.

Does BMI work for athletes?

BMI can overestimate weight-related risk in muscular athletes because it does not distinguish muscle from fat.

Is BMI different for men and women?

The adult BMI formula and standard categories are the same for men and women, but body composition can differ.

Is BMI different for children?

Yes. Children and teens use BMI-for-age percentiles based on age and sex, not fixed adult BMI ranges.

Why is BMI important?

BMI is quick, inexpensive, and widely used for screening weight status and monitoring population health trends.

Can BMI predict disease?

BMI can be associated with health risks at a population level, but it cannot diagnose disease or predict an individual's future health by itself.

What are BMI limitations?

BMI may be misleading for athletes, older adults, pregnant people, children, and some ethnic populations.

How often should I calculate BMI?

Occasional checks can help monitor weight trends, but frequent BMI checks are usually less useful than long-term patterns and clinical context.

What should I do if my BMI is high?

Consider discussing the result with a qualified healthcare professional, especially if you have symptoms, medical conditions, or medication questions.

What should I do if my BMI is low?

A low BMI can have many causes. A healthcare professional can help review nutrition, medical history, and any concerning symptoms.

Can I use this BMI calculator during pregnancy?

Adult BMI categories are not designed to interpret pregnancy weight changes. Use pregnancy-specific guidance from a clinician.

More Tools

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Glossary

Key Terms

BMI
A number calculated from height and weight to estimate adult weight status.
Body Mass Index
The full name for BMI.
Underweight
An adult BMI below 18.5.
Healthy Weight
An adult BMI from 18.5 to 24.9.
Overweight
An adult BMI from 25.0 to 29.9.
Obesity
An adult BMI of 30.0 or higher.
Metric Units
Centimeters and kilograms in this calculator.
Imperial Units
Feet, inches, and pounds in this calculator.
Body Composition
The body's mix of fat, muscle, bone, and other tissues.
Screening Tool
A quick check that may indicate whether more assessment is useful.

Sources

References

Health & Medical Notice

Medical & Educational Disclaimer

Non-Clinical Estimate

This BMI calculator is for informational and educational purposes only. BMI is a screening tool, not a diagnosis of disease, body fat, or individual health. Speak with a qualified healthcare professional for personalized medical advice, especially for children, pregnancy, eating concerns, chronic disease, or major weight changes.

Calculations and transformations execute locally on your machine with full offline support. Always verify critical results.

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