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BMI Calculator

Calculate your Body Mass Index (BMI) and health category based on WHO standards.

Reviewed & Maintained by
Aadil Malik — Software Engineer
1 min read  ·  158 words

What is a BMI Calculator?

A Body Mass Index (BMI) calculator is an internationally recognized anthropometric screening metric established by the World Health Organization (WHO) to evaluate body weight relative to stature.

BMI Formulas (Metric & Imperial)

  • Metric: $$\text{BMI} = \frac{\text{Weight (kg)}}{\left[\text{Height (m)}\right]^2}$$
  • Imperial: $$\text{BMI} = 703 \times \frac{\text{Weight (lbs)}}{\left[\text{Height (inches)}\right]^2}$$

WHO BMI Classification Table

BMI RangeCategoryHealth Risk Profile
< 18.5UnderweightNutritional deficiency, immune vulnerability
18.5 – 24.9Normal WeightLowest cardiovascular & metabolic risk
25.0 – 29.9OverweightModerate risk for hypertension & insulin resistance
30.0 – 34.9Obese Class IHigh cardiovascular risk
35.0 – 39.9Obese Class IIVery high metabolic risk
40.0+Obese Class IIISevere / Extreme risk

Frequently Asked Questions

BMI is a numerical value derived from mass (weight) and height. It serves as a screening tool to categorize individuals as underweight, normal weight, overweight, or obese according to World Health Organization (WHO) standards.
Metric formula: BMI = weight (kg) / [height (m)]^2. Imperial formula: BMI = 703 * weight (lbs) / [height (inches)]^2.
Underweight: BMI < 18.5; Normal weight: BMI 18.5–24.9; Overweight: BMI 25.0–29.9; Obese Class 1: BMI 30.0–34.9; Obese Class 2: BMI 35.0–39.9; Obese Class 3: BMI 40.0+.
No. BMI does not differentiate between lean muscle, bone density, and body fat. Muscular athletes often register as 'overweight' despite having very low body fat percentages.
For adult men and women, a healthy BMI ranges between 18.5 and 24.9.
For children and teens (ages 2–20), BMI is age-and-gender specific (BMI-for-age percentiles). For older adults (65+), slightly higher BMIs (25–27) are associated with lower mortality.
Waist-to-hip ratio, body fat percentage (DEXA or caliper), blood pressure, lipid panels, and resting heart rate provide a comprehensive health picture.
Creating a sustainable caloric deficit of 300–500 kcal/day through a nutrient-dense whole foods diet combined with resistance training and cardiovascular exercise safely reduces fat mass.