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BMI calculator (and what it misses)

Work out your body mass index (BMI) in pounds and feet or kilograms and centimeters, see which WHO category it falls in, and what it does not measure: how much of your weight is fat and how much is muscle, or where that fat is.

For adults. The math runs in your browser: nothing you type is sent anywhere.

Weight

67 to 661 lb (30 to 300 kg); decimals are fine.

Height

Fill in the form and press “Calculate” to see your result here.

What BMI does not measure

  • How much of your weight is fat. According to the CDC, BMI does not distinguish between fat, muscle, and bone. The WHO calls it a “surrogate marker” of body fat.
  • Where the fat is. The CDC adds that it does not show where in the body fat is stored. According to the NHLBI, part of the NIH, carrying it mostly around the waist rather than the hips raises the risk of heart disease and type 2 diabetes, and a waist of more than 35 inches (about 88 cm) for women or more than 40 inches (about 102 cm) for men raises it. The WHO mentions waist circumference as a measure that helps with diagnosis.
  • It misses part of excess body fat. In a meta-analysis of 25 studies with 31,968 people in whom body fat was measured directly, the usual BMI cutoffs for obesity rarely flagged people without excess fat (specificity of 90%), but only caught half of those who had it (sensitivity of 50%).
  • Where you come from. A WHO expert consultation (2004) concluded that in Asian populations the risk of type 2 diabetes and cardiovascular disease rises at lower BMIs: between 22 and 25, depending on the population. It kept the international classification and proposed additional action points at 23, 27.5, 32.5, and 37.5.
  • Age. In a meta-analysis of 32 studies with 197,940 people aged 65 or older, a BMI of 25 to 29.9 was not associated with higher mortality; risk rose below 23 and above 33.
  • Children and teens. From 5 to 19 years, the WHO does not use these categories but its growth references (BMI-for-age), and the CDC uses BMI-for-age percentiles from age 2. This calculator is not for people under 18.

The 2025 Lancet commission proposes confirming excess body fat with a direct measurement or with at least one other body measurement, such as waist circumference, waist-to-hip ratio, or waist-to-height ratio. Above a BMI of 40 it takes excess fat as given.

How drug labels use BMI

In the United States, the FDA labels of Wegovy and Zepbound (the tirzepatide brand for weight; in the US, Mounjaro is approved only for type 2 diabetes) describe adults with obesity, or with overweight and at least one weight-related condition. The trials they describe defined those groups with the same cutoffs: a BMI of 30 or higher, or of 27 to less than 30. For adolescents, Wegovy does not use these cutoffs but obesity defined as a BMI at or above the 95th percentile for age and sex, from age 12; in the European Union, also with a body weight above 60 kg.

In the European Union, the labels (summaries of product characteristics) of Wegovy and Mounjaro indicate these medicines for weight management, together with a reduced-calorie diet and more physical activity, in adults with a BMI of 30 or higher, or of 27 to less than 30 with at least one weight-related condition, such as high blood pressure, dyslipidemia (high cholesterol or triglycerides), obstructive sleep apnea, cardiovascular disease, prediabetes, or type 2 diabetes.

Whether a treatment fits you is your doctor’s call. A BMI above or below those numbers does not, on its own, decide whether a medication is right for you: your medical history, other conditions, and other medicines all count. That is why this calculator does not tell you whether you “qualify” for anything.

How it is calculated

Formula. BMI = weight in kilograms ÷ (height in meters × height in meters), expressed in kg/m². In pounds and inches it is the same as weight in pounds × 703 ÷ (height in inches × height in inches). For example, 154 lb and 5 ft 6 in (66 in): 154 × 703 ÷ (66 × 66) = 24.9.

Units. One pound is 0.45359237 kg and one inch is 2.54 cm; a foot is 12 inches. We convert pounds and feet to kilograms and centimeters first, and accept 67 to 661 lb (30 to 300 kg) and 4 ft 0 in to 7 ft 6 in (120 to 230 cm).

Rounding. We show BMI with one decimal and assign the category from that rounded number, so the figure and the category always match.

Classification of adults by BMI (WHO, 2000)
WHO categoryBMI (kg/m²)
Underweightunder 18.5
Normal range18.5 to 24.9
Pre-obese (part of what the WHO calls overweight)25.0 to 29.9
Obese class I30.0 to 34.9
Obese class II35.0 to 39.9
Obese class III40.0 or higher

This is table 2.1 of WHO Technical Report 894. The report states that the cutoffs are the same for women and men and for all adult ages, and that the same BMI may not correspond to the same amount of fat in different populations. The WHO calls a BMI of 25.0 or higher overweight, and one of 30.0 or higher obesity. The CDC uses the same adult cutoffs, with “healthy weight” for 18.5 to 24.9 and obesity classes 1 to 3.

What it does not do. It does not calculate an “ideal weight” or the weight that would give another BMI, and it does not suggest diets. A shared link fills in the form with the weight and height it carries; while you type, those values are not stored in the page address.

Further reading

Sources

Guidelines and papers the calculation is based on, with the access date.

  1. Clinical guidelineWorld Health Organization.Obesity: preventing and managing the global epidemic. Report of a WHO consultation. WHO Technical Report Series 894 (2000), table 2.1.accessed .
  2. InstitutionWorld Health Organization.Obesity and overweight (fact sheet).accessed .
  3. Clinical guidelineThe Lancet.WHO Expert Consultation. Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. Lancet. 2004;363(9403):157-163.accessed .
  4. Clinical guidelineThe Lancet Diabetes & Endocrinology.Rubino F, Cummings DE, Eckel RH, et al. Definition and diagnostic criteria of clinical obesity. Lancet Diabetes Endocrinol. 2025;13(3):221-262.accessed .
  5. Meta-analysisInternational Journal of Obesity.Okorodudu DO, Jumean MF, Montori VM, et al. Diagnostic performance of body mass index to identify obesity as defined by body adiposity: a systematic review and meta-analysis. Int J Obes. 2010;34(5):791-799.accessed .
  6. Meta-analysisThe American Journal of Clinical Nutrition.Winter JE, MacInnis RJ, Wattanapenpaiboon N, Nowson CA. BMI and all-cause mortality in older adults: a meta-analysis. Am J Clin Nutr. 2014;99(4):875-890.accessed .
  7. InstitutionCenters for Disease Control and Prevention (CDC).About Body Mass Index (BMI).accessed .
  8. InstitutionNational Heart, Lung, and Blood Institute (NIH).Healthy Weight: measuring waist circumference.accessed .
  9. Drug labelEuropean Medicines Agency (EMA).Wegovy (semaglutide): EU summary of product characteristics (EPAR product information), section 4.1.accessed .
  10. Drug labelEuropean Medicines Agency (EMA).Mounjaro (tirzepatide): EU summary of product characteristics (EPAR product information), section 4.1.accessed .
  11. Drug labelFDA (DailyMed, NIH).Wegovy (semaglutide) injection and tablets, prescribing information, revised 6/2026, sections 1 and 14.accessed .
  12. Drug labelFDA (DailyMed, NIH).Zepbound (tirzepatide) injection, prescribing information, revised 8/2026, sections 1 and 14.accessed .
  13. Drug labelFDA (DailyMed, NIH).Mounjaro (tirzepatide) injection, prescribing information, revised 8/2026, section 1.accessed .