BMI calculator
Calculate your Body Mass Index from height and weight in any unit combination. See your BMI category benchmarked against WHO, South Asian, and East Asian thresholds.
What is the BMI Calculator?
This BMI calculator works out your body mass index from your height and weight, with a twist: each input has its own unit toggle. You can enter your height in centimeters and your weight in pounds, or your height in feet and inches and your weight in kilograms — whatever combination matches how you actually think about your measurements. The tool recalculates instantly as you type, showing your BMI value, which category you fall into, and the healthy weight range for your height.
How is BMI calculated?
BMI uses a simple formula: BMI = kg / m². Take your weight in kilograms and divide it by the square of your height in meters. A person who weighs 68 kg and stands 1.70 m tall has a BMI of 68 / (1.70 × 1.70) = 23.5. For imperial units, the equivalent formula is BMI = (lb / in²) × 703. The math is standardized worldwide — the same formula is used by every health organization and clinical setting on the planet.
Why multiple threshold sets?
The original WHO BMI categories were developed from studies of predominantly European populations. Research over the past two decades has shown that health risks associated with a given BMI level are not uniform across ethnic groups. South Asian populations tend to accumulate more visceral fat at lower BMI values, meaning metabolic conditions like type 2 diabetes can appear at a BMI that would be considered "normal" under WHO standards. The South Asian cutoffs (normal up to 23, overweight 23–27.5) reflect guidelines adopted by medical bodies in India, Pakistan, and Bangladesh. Similarly, East Asian populations — particularly in Japan, China, and South Korea — face elevated cardiovascular risk at lower BMI thresholds, leading to adjusted categories (normal up to 24, overweight 24–28). This calculator lets you switch between all three sets so you can see how your BMI reads under the thresholds most relevant to your background.
What BMI doesn't tell you
BMI is a screening tool, not a diagnosis. It measures weight relative to height but cannot distinguish between muscle and fat. Athletes with high muscle mass often classify as "overweight" by BMI while being metabolically healthy. Conversely, someone with a "normal" BMI can carry excess visceral fat — sometimes called "skinny fat" — and face elevated health risks. BMI also doesn't account for age, sex, bone density, or fat distribution. For older adults, a slightly higher BMI is often associated with better outcomes. For a fuller picture, clinicians use BMI alongside waist circumference, body fat percentage, blood markers, and clinical history.
"The proportion of Asian people with a high risk of type 2 diabetes and cardiovascular disease is substantial at BMIs lower than the existing WHO cut-off point for overweight (≥25 kg/m²)."
"Classifying an individual as lean, when in fact the individual is truly obese, may put this individual at risk for diseases associated with obesity."
BMI Ranges: WHO vs South Asian vs East Asian Standards
South Asian and East Asian populations face higher metabolic risk at lower BMI values, so their diagnostic thresholds are set below the global WHO standard.
| Category | WHO | South Asian Lower cutoffs | East Asian Lower cutoffs |
|---|---|---|---|
| Underweight | < 18.5 | < 18.5 | < 18.5 |
| Normal weight | 18.5 – 24.9 | 18.5 – 22.9 | 18.5 – 22.9 |
| Overweight | 25.0 – 29.9 | 23.0 – 24.9 | 23.0 – 27.4 |
| Obese (Class I) | 30.0 – 34.9 | 25.0 – 29.9 | ≥ 27.5 |
| Obese (Class II) | 35.0 – 39.9 | ≥ 30.0 | — |
| Obese (Class III) | ≥ 40.0 | — | — |
Source: WHO Expert Consultation on BMI (2004). Consult a physician for clinical diagnosis.
Common Uses
- General health check-ins: Use BMI as a quick annual baseline to track whether your weight relative to height is trending toward a healthy range.
- Insurance underwriting: Life and health insurers use BMI as an underwriting factor — know your BMI before applying to estimate premium categories.
- Pre-surgery assessment: Surgeons often require BMI below a threshold (commonly 35–40) before elective procedures like joint replacement or bariatric surgery.
- Fitness goal setting: Calculate the target weight needed to move into a specific BMI category and use it as a concrete fitness milestone.
- Paediatric growth tracking: The calculator supports metric and imperial inputs for tracking children's growth against age-adjusted BMI percentile charts.
- Clinical research and trials: Many clinical studies use BMI as an inclusion or exclusion criterion — verify eligibility before enrolling.
- Nutritional planning: Dietitians use BMI alongside waist circumference and other markers to tailor calorie targets and macronutrient ratios.
FAQ
What is a healthy BMI?
Under WHO standards, a BMI between 18.5 and 25 is considered normal weight. However, the healthy range depends on your ethnic background — South Asian guidelines consider 18.5 to 23 normal, and East Asian guidelines use 18.5 to 24. This calculator lets you switch between all three threshold sets.
Why does my BMI show overweight but I'm muscular?
BMI cannot distinguish muscle from fat. If you have significant muscle mass from training, your BMI will read higher than someone of the same height with more body fat and less muscle. Athletes and regular weightlifters often classify as overweight or even obese by BMI alone while being metabolically healthy.
Do Indians use different BMI cutoffs?
Yes. Indian medical guidelines, along with those in Pakistan and Bangladesh, use lower BMI cutoffs because South Asian populations tend to develop metabolic conditions at lower body weights. The South Asian thresholds in this calculator reflect those adjusted guidelines: normal up to 23, overweight 23 to 27.5.
How do I calculate BMI manually?
Divide your weight in kilograms by the square of your height in meters. For example, if you weigh 70 kg and you're 1.75 m tall: 70 / (1.75 × 1.75) = 22.9. If you use pounds and inches, multiply (weight in lb / height in inches squared) by 703.
Does the BMI calculator store my health data?
No. Your height and weight are processed entirely in your browser. Nothing is sent to a server or stored after you close the page.
Can children and teenagers use this BMI calculator?
This calculator uses standard adult BMI formulas. BMI for children and teens is age- and sex-specific — please use a pediatric BMI chart or consult a doctor for accurate assessment.
By the Numbers
- The WHO defines a BMI of ≥30 as obese and 18.5–24.9 as the healthy normal range
- 42.4% of U.S. adults are classified as obese based on 2017–2018 NHANES data (CDC)
- Globally, obesity rates have nearly tripled since 1975 (WHO Global Health Observatory)
- A BMI of 25+ is associated with a 50% increased risk of developing type 2 diabetes (NIH clinical guidelines)