BMI Calculator

Calculate your Body Mass Index and find your healthy weight range

Instant results | Free to use

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BMI Categories

  • Underweight < 18.5
  • Normal 18.5 – 24.9
  • Overweight 25.0 – 29.9
  • Obese ≥ 30.0

BMI Formulas

  • Metric

    BMI = kg / m²

  • Imperial

    BMI = (lbs × 703) / in²

Important Note

BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, age, or sex. Consult a healthcare professional for a comprehensive health assessment.

What Is BMI?

Understanding Body Mass Index and what it means for your health

Body Mass Index (BMI) is a numerical value derived from your weight and height. Developed by Belgian mathematician Adolphe Quetelet in the 1830s, it provides a simple screening method to categorize individuals into weight status groups: underweight, normal weight, overweight, and obese.

BMI is widely used by healthcare professionals, public health organizations, and researchers because it is easy to calculate and correlates reasonably well with body fat levels at the population level. However, it is not a direct measure of body fat and has known limitations for certain individuals.

The Formula

BMI is calculated by dividing weight in kilograms by height in meters squared. It produces a single number that can be compared against standard thresholds to determine weight status.

Limitations

BMI cannot distinguish between muscle and fat mass. Athletes, elderly individuals, and pregnant women may receive misleading results. It also does not account for fat distribution or ethnicity.

WHO Classification

The World Health Organization defines standard BMI thresholds used internationally. These categories help public health officials track obesity trends and assess population-level health risks.

BMI Categories & Health Risk

WHO classification of BMI ranges and associated health implications

Category BMI Range Health Risk Indicator
Severe Underweight < 16.0 Severe risk of nutritional deficiency
Underweight 16.0 – 18.4 Increased risk of nutritional deficiency
Normal Weight 18.5 – 24.9 Low risk (healthy range)
Overweight 25.0 – 29.9 Increased risk of cardiovascular disease
Obese Class I 30.0 – 34.9 High risk of cardiovascular disease
Obese Class II 35.0 – 39.9 Very high risk of health complications
Obese Class III ≥ 40.0 Extremely high risk of health complications

BMI Formula Explained

How to calculate BMI using metric and imperial measurements

Metric Formula

BMI = weight (kg) ÷ height (m)²

Example: Weight = 70 kg, Height = 1.75 m

BMI = 70 ÷ (1.75 × 1.75) = 70 ÷ 3.0625 = 22.86

Imperial Formula

BMI = (weight (lbs) × 703) ÷ height (in)²

Example: Weight = 154 lbs, Height = 5'9" (69 in)

BMI = (154 × 703) ÷ (69 × 69) = 108,262 ÷ 4,761 = 22.74

What Is BMI Prime?

BMI Prime = BMI ÷ 25

BMI Prime is the ratio of your BMI to the upper limit of the normal range (25). A BMI Prime of 1.0 means you are at the upper boundary of normal weight. Values below 1.0 indicate normal or underweight, while values above 1.0 indicate overweight or obese. This makes it easy to see how far above or below the healthy threshold you are.

Frequently Asked Questions

Common questions about BMI and body weight assessment

A healthy BMI falls between 18.5 and 24.9, according to the World Health Organization. This range is associated with the lowest risk of weight-related diseases such as type 2 diabetes, heart disease, and certain cancers. However, the ideal BMI can vary by age, sex, and ethnicity.
No, BMI has significant limitations for muscular individuals. Because it only considers weight and height, it cannot differentiate between lean muscle mass and body fat. A bodybuilder with very low body fat may be classified as "overweight" or "obese" by BMI. For athletes, body fat percentage measurements or DEXA scans are more appropriate.
BMI is interpreted differently for children and teens (ages 2-19). Instead of fixed thresholds, their BMI is compared against age- and sex-specific growth charts to determine a percentile ranking. A child at the 85th-95th percentile is considered overweight, and above the 95th percentile is considered obese.
A BMI of 25 or above is associated with increased risk of cardiovascular disease, type 2 diabetes, high blood pressure, sleep apnea, certain cancers, and joint problems. The risk increases progressively with higher BMI values. However, BMI alone does not determine health; other factors like diet, activity level, and family history matter too.
Several metrics complement or improve upon BMI: Waist circumference measures abdominal fat, which is a stronger predictor of heart disease risk. Waist-to-hip ratio considers body fat distribution. Body fat percentage directly measures fat mass. DEXA scans provide detailed body composition analysis. Using multiple metrics gives a more complete picture of health.
Research has shown that health risks associated with excess weight vary by ethnicity. For example, Asian populations tend to develop health complications at lower BMI values, so some health organizations recommend a lower overweight threshold of 23 for Asian adults. Conversely, some Pacific Islander populations may have lower risk at higher BMI values due to differences in body composition.