How is BMI calculated?

BMI is calculated by dividing body weight in kilograms by the square of height in metres. The formula is: BMI = Weight (kg) ÷ Height² (m²). For imperial units, multiply [Weight (lbs) ÷ Height² (in²)] by 703.

What is a normal BMI range?

According to the World Health Organization (WHO), a BMI between 18.5 and 24.9 kg/m² is considered normal weight for adults. However, Asian populations may have different risk thresholds, with overweight starting at BMI ≥ 23.

Is BMI accurate for athletes or muscular individuals?

BMI may overestimate body fat in athletes or individuals with high muscle mass, as it does not distinguish between fat and lean tissue. Additional assessments such as body composition analysis, skinfold measurements, or DEXA scanning may be more appropriate.

Can BMI be used for children?

For children and adolescents (ages 2–19), BMI is calculated the same way but interpreted using age- and sex-specific percentile charts (CDC or WHO growth charts) rather than the fixed adult categories.

What BMI indicates obesity?

A BMI of 30.0 kg/m² or higher is classified as obese by WHO standards. Obesity is further categorized into Class I (30.0–34.9), Class II (35.0–39.9), and Class III or morbid obesity (≥ 40.0).

Medically Reviewed · CliniqWise Clinical Advisory Board · Updated 2026-08-27

Body Mass Index (BMI) Calculator

Estimate body mass index from height and weight for basic body assessment.

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BMI Calculator

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This calculator is for informational and educational purposes. Results should be interpreted with clinical judgment and local guidelines.

What is Body Mass Index (BMI)?

Body Mass Index (BMI) is a numerical value derived from a person's height and weight. It is calculated by dividing weight in kilograms by the square of height in metres (kg/m²). BMI is widely used as a screening tool to categorize individuals into weight status categories — underweight, normal weight, overweight, and obese — and to identify potential health risks associated with body weight.

BMI = Weight (kg) ÷ Height² (m²). A BMI of 18.5–24.9 is considered normal weight by WHO standards.

When to Use the BMI Calculator

Routine health screening in OPD and general practice settings.
Initial assessment of weight status during annual health check-ups.
Population-level obesity surveillance and public health research.
Nutritional assessment before initiating diet or exercise interventions.
Pre-operative risk assessment where obesity is a relevant co-morbidity.
Monitoring weight trends over time in chronic disease management (e.g., diabetes, hypertension, metabolic syndrome).
Pediatric growth monitoring (using age- and sex-specific BMI percentiles for children 2–19 years).

Obesity screeningType 2 diabetes risk assessmentCardiovascular disease risk stratificationMetabolic syndrome evaluationMalnutrition screening in elderly patients

BMI Formula

Metric System

BMI = Weight (kg) ÷ Height² (m²)

Example: 70 kg ÷ (1.75 m)² = 70 ÷ 3.0625 = 22.86 kg/m²

Imperial System

BMI = [Weight (lbs) ÷ Height² (in²)] × 703

Example: [154 lbs ÷ (68.9 in)²] × 703 = 22.86 kg/m²

Variables

Weight (kg or lbs)

Total body weight of the patient.

Height (m, cm, or inches)

Standing height of the patient.

The BMI formula was devised by Belgian mathematician Adolphe Quetelet in the 1830s and is sometimes called the Quetelet Index. It does not directly measure body fat but correlates with more direct measures of body fat such as DEXA scanning.

BMI Classification – WHO Categories

The World Health Organization (WHO) provides standard BMI categories for adults aged 20 and above. These classifications apply to both men and women.

Range	Classification	Health Risk
< 16.0	Severe Thinness	High
16.0 – 16.9	Moderate Thinness	Moderate
17.0 – 18.4	Mild Thinness	Low–Moderate
18.5 – 24.9	Normal Weight	Average
25.0 – 29.9	Overweight (Pre-Obese)	Increased
30.0 – 34.9	Obese Class I	High
35.0 – 39.9	Obese Class II	Very High
≥ 40.0	Obese Class III (Morbid)	Extremely High

Asian populations may have different risk thresholds. The WHO Western Pacific Region and the Indian Association of Clinical Medicine recommend lower cut-offs: ≥ 23 for overweight and ≥ 25 for obese in South Asian populations.

Limitations & Clinical Warnings

BMI does not differentiate between fat mass, muscle mass, and bone density. Muscular individuals (e.g., athletes) may be classified as overweight or obese despite having low body fat.

BMI does not account for fat distribution. Abdominal (visceral) fat is more strongly associated with cardiovascular and metabolic disease than subcutaneous fat, and BMI cannot capture this distinction.

Age, sex, and ethnicity affect the relationship between BMI and body fat percentage. Standard cut-offs may not accurately reflect health risks across all populations.

BMI is not reliable for pregnant women, individuals with edema, very short (< 150 cm) or very tall (> 190 cm) adults, amputees, or patients with significant fluid retention.

BMI is a screening tool, not a diagnostic tool. A comprehensive clinical assessment should include waist circumference, waist-to-hip ratio, body composition analysis, medical history, and laboratory findings.

Elderly patients may have a "normal" BMI but elevated body fat percentage due to age-related loss of muscle mass (sarcopenia).

Medical Disclaimer

This calculator is for informational and educational purposes only. It does not replace clinical judgment, physical examination, or individualized patient assessment. Always interpret BMI alongside the complete clinical picture and current local guidelines.

References & Citations

World Health Organization. “Obesity: preventing and managing the global epidemic”. WHO Technical Report Series. 2000. 894: i-xii, 1-253. PMID: 11234459
Keys A, Fidanza F, Karvonen MJ, Kimura N, Taylor HL. “Indices of relative weight and obesity”. Journal of Chronic Diseases. 1972. 25(6-7): 329-343. DOI: 10.1016/0021-9681(72)90027-6
National Heart, Lung, and Blood Institute (NHLBI). “Clinical Guidelines on the Identification, Evaluation, and Treatment of Overweight and Obesity in Adults”. NIH Publication. 1998. No. 98-4083. NIH/NHLBI
Misra A, Chowbey P, Makkar BM, et al.. “Consensus Statement for Diagnosis of Obesity, Abdominal Obesity and the Metabolic Syndrome for Asian Indians”. Journal of the Association of Physicians of India. 2009. 57: 163-170. PMID: 19582986

Medically Reviewed

Reviewed by CliniqWise Clinical Advisory Board · Last updated: 2026-08-27 · Next review: 2027-02-27

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