Printed on 3/17/2026
For informational purposes only. This is not medical advice.
Body Mass Index (BMI) is the standard screening measurement used by healthcare providers worldwide to assess weight status. Our calculator uses the World Health Organization's formula to instantly categorize your weight as underweight, normal, overweight, or obese — providing context on associated health risks and next steps.
Formula: BMI = weight (kg) / height (m)²
Input your height (in cm or feet/inches) and weight (in kg or lbs). Use the unit toggle to switch between metric and imperial systems.
Your Body Mass Index is calculated instantly using the WHO formula: BMI = weight (kg) ÷ height (m)². Results display your numeric BMI value.
See where you fall on the BMI scale — underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), or obese (≥30) — with insights on what your result means.
Healthcare providers
Physicians use BMI during routine checkups as a quick flag for patients who may benefit from nutritional counseling, further metabolic workup, or weight management referrals.
Dietitians & nutritionists
Registered dietitians calculate BMI as part of initial assessments before creating meal plans, tracking progress, or setting caloric targets for clients. Use [TDEE Calculator](/tools/tdee-calculator) for personalized daily calorie needs and [Macro Calculator](/tools/macro-calculator) for balanced macronutrient distribution.
Personal trainers & athletes
Trainers use BMI alongside body fat percentage and waist measurements to establish baseline metrics and track body composition changes during programs.
Researchers & epidemiologists
BMI is the standard metric in population health studies, enabling researchers to compare obesity prevalence across demographics and track trends over time.
Individuals tracking health
Anyone monitoring their weight can use BMI to set realistic goals, understand their current category, and track progress during diet or exercise programs. Calculate your [Ideal Weight](/tools/ideal-weight) for science-based goal targets and [Calorie Calculator](/tools/calorie-calculator) for weight loss or gain strategies.
HR & corporate wellness
Companies include BMI assessments in employee wellness programs to identify population health trends and measure the impact of wellness initiatives.
You're tallest after sleep. Spinal compression throughout the day can reduce height by 1–2 cm, which affects your BMI calculation. For consistency, measure at the same time.
Don't mix metric and imperial within a calculation. If you know your height in feet/inches, convert fully to cm before entering, or use our unit toggle for automatic conversion.
Same time of day, same scale, minimal clothing. Morning after using the bathroom provides the most reliable baseline. Avoid weighing after meals or intense exercise.
If weighing with clothes on, subtract approximately 0.5–1 kg for typical indoor clothing. Shoes, heavy jackets, and accessories add significant weight.
Daily weight fluctuates 1–2 kg from hydration, sodium intake, and digestion. A single BMI reading matters less than your trend over weeks or months.
Asian populations may need lower BMI thresholds (overweight ≥23, obese ≥27.5) due to higher metabolic risk at lower BMI. Discuss appropriate targets with your doctor.
Waist circumference or [waist-to-hip ratio](/tools/waist-to-hip-ratio) often predicts cardiovascular risk better than BMI alone. A waist >102 cm (men) or >88 cm (women) indicates elevated risk regardless of BMI. Also consider [waist-to-height ratio](/tools/waist-to-height-ratio) and assess CV risk with [ASCVD Risk Calculator](/tools/ascvd-risk).
If you have significant muscle mass, BMI may classify you as overweight despite low body fat. Use our [Body Fat Calculator](/tools/body-fat-calculator) for a more complete picture.
BMI identifies who might need further evaluation — it's not a diagnosis. Elevated BMI should prompt discussion with a healthcare provider, not immediate alarm.
BMI norms vary by ethnicity, age, and sex. A 'healthy' BMI for a 25-year-old may differ from optimal ranges for older adults, where slightly higher BMI (25–27) may be protective.
This calculator uses the World Health Organization's standard BMI formula, established in the 1995 WHO Technical Report Series 854 and reaffirmed in subsequent guidelines. The methodology has been validated in thousands of epidemiological studies and remains the primary screening tool recommended by the CDC, NIH, and major medical organizations worldwide.
Your BMI falls into one of several standard categories defined by the World Health Organization (WHO). A BMI under 18.5 is classified as underweight, which may indicate malnutrition or an underlying health condition. A BMI between 18.5 and 24.9 is considered normal weight and is generally associated with the lowest health risks. A BMI of 25 to 29.9 falls in the overweight range and may signal increased risk for conditions like heart disease and type 2 diabetes. A BMI of 30 or above is classified as obese — further divided into Class I (30–34.9), Class II (35–39.9), and Class III (40+) — and carries a significantly elevated risk of metabolic and cardiovascular disease.
Keep in mind that BMI is a population-level screening metric, not a diagnosis. Two people with the same BMI can have very different body compositions, fitness levels, and health profiles. Your result should be interpreted alongside other measurements and clinical context.
BMI is most useful as a quick, first-pass screening tool during routine health check-ups or when you want a general sense of whether your weight is proportionate to your height. Clinicians commonly use it in primary care, public health surveillance, and epidemiological research to identify individuals who may benefit from further evaluation.
It is also helpful for tracking weight trends over time — for example, monitoring changes during a weight management program or after a lifestyle intervention.
BMI does not distinguish between fat mass and lean mass. Athletes and individuals with high muscle mass may be classified as overweight or obese despite having low body fat. Conversely, older adults who have lost muscle mass may have a normal BMI but carry excess fat.
BMI also does not reflect fat distribution. Central (abdominal) obesity is a stronger predictor of cardiovascular risk than overall weight, and BMI misses this distinction entirely. Waist circumference or waist-to-hip ratio may be more informative in these cases.
Additionally, standard BMI thresholds were developed primarily from data on European populations. The WHO recommends lower cut-offs for some Asian populations (overweight ≥ 23, obese ≥ 27.5) because metabolic risk increases at lower BMI levels in these groups.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
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Body MetricsCalculate your waist-to-hip ratio (WHR) to assess cardiovascular disease risk. A simple measurement used by the WHO as a health indicator.
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