All tools

BMI Calculator

Calculate adult BMI in metric or imperial units, see WHO weight categories and a reference healthy weight range for your height.

Measurements

Your BMI

BMI
—
BMI category
—
Reference weight range (BMI 18.5–24.9)
—

Adults only. BMI is a screening measure and the result is strictly informative; it in no way replaces the guidance, diagnosis or follow-up of a qualified healthcare professional.

How BMI is calculated and what it means

Body mass index (BMI) compares weight with height and is used as a first step in adult health screening. It can help start a conversation about health, but it does not directly measure body fat or diagnose a condition. Read the result together with your health history, body composition and advice from a qualified healthcare professional.

BMI formula, units and precision

  1. Convert height to meters: Divide centimeters by 100. A height of 175 cm is 1.75 m. Square the height by multiplying it by itself: 1.75 × 1.75 = 3.0625 m².
  2. Divide weight by height squared: BMI = weight (kg) ÷ height (m)². For 70 kg and 175 cm, 70 ÷ 3.0625 = 22.857142… kg/m², displayed as 22.86.
  3. Use exact imperial conversions: Feet and inches are combined as total inches = feet × 12 + inches. The calculator converts using 1 in = 0.0254 m and 1 lb = 0.45359237 kg, then applies the same metric formula. The familiar imperial multiplier of 703 is an approximation.
  4. Round only for display: Intermediate values are not deliberately rounded. BMI and reference weights are displayed to two decimal places, while the category uses the unrounded result. For example, a BMI of 24.999 is displayed as 25.00 but remains in the normal-weight category. Measurement accuracy still matters; extra decimals do not make a scale or height measurement more accurate.

Standard WHO adult BMI classification

  • Underweight: BMI below 18.5.
  • Normal weight: BMI from 18.5 to below 25.
  • Overweight: BMI from 25 to below 30.
  • Obesity class I: BMI from 30 to below 35.
  • Obesity class II: BMI from 35 to below 40.
  • Obesity class III: BMI of 40 or above. These are standard WHO adult categories, not individual diagnoses; local clinical guidance may use different risk thresholds for some populations.

Understanding the reference weight range

  • Understanding the reference weight range: The tool uses BMI 18.5–24.9: minimum weight = 18.5 × height (m)² and maximum weight = 24.9 × height (m)². At 1.75 m, that is approximately 56.66–76.26 kg. Imperial results are converted to pounds. The displayed range uses 24.9 as its upper reference, while the normal-weight category extends to below 25. This is a general reference, not a prescribed goal or proof of good health.

Practical habits for a balanced lifestyle

  • Eat a varied, balanced diet: Include vegetables, fruit, whole grains and suitable protein sources. Choose sustainable eating habits rather than restrictive diets or rapid weight changes.
  • Move regularly: Combine everyday movement with aerobic activity and muscle-strengthening exercise suited to your ability. Start gradually if you are inactive or have a health condition.
  • Support recovery: Keep a regular sleep routine, stay hydrated and make time for stress management. Health is broader than a single weight or BMI reading.
  • Seek personalized guidance: Discuss an unexpected result, unexplained weight change or concerns about eating with a healthcare professional. Review weight trends and other health measures instead of treating the reference range as a target to reach at any cost.

BMI limitations and common questions

Can athletic muscle mass raise BMI?

Yes. BMI cannot distinguish muscle, fat and bone, or show where body fat is stored. A muscular athlete may have a high BMI without excess body fat, while someone in the normal range may still have health risks. Waist measurements, clinical history and other assessments can add context.

Does age affect interpretation?

Adult categories are not a substitute for age- and sex-specific growth assessment in children and teenagers. In older adults, changes in muscle mass and body composition can make BMI alone less informative. The same number should not automatically lead to the same recommendation for everyone.

Is this calculator suitable during pregnancy?

Do not use your current pregnancy weight with these categories to judge your health or set a weight-loss goal. Pregnancy changes weight and body composition. A clinician may use pre-pregnancy BMI alongside pregnancy-specific guidance.

Does a normal BMI guarantee good health?

No. BMI is one screening measure, not a diagnosis. Ethnic background, medical conditions and body composition can affect its interpretation. Blood pressure, relevant tests, fitness, nutrition and wellbeing also matter; discuss your overall picture with a healthcare professional.

Medical Authority & Weight Standards

The weight categories and reference ranges used in this tool are strictly based on the official guidelines and classification standards established by the World Health Organization (WHO). You can review the official parameters directly on the WHO Global Health Observatory.

Important Medical Disclaimer

This BMI calculator is a general screening tool and is strictly informative. It does not measure body fat percentage and does not replace professional medical advice, diagnosis, or clinical evaluation. Any changes to your diet or exercise routine should be supervised by a doctor, nutritionist, or qualified healthcare professional. For official health standards, please refer to the WHO Health Topics on Obesity.