Bmi Calculator
Calculate your Body Mass Index with metric or imperial units
What Is BMI and What Do the Numbers Mean?
Body Mass Index (BMI) is a simple screening tool that estimates body fat based on height and weight. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is still used by the World Health Organization as a population-level health indicator. While BMI does not directly measure body fat percentage, it provides a quick, cost-free way to identify potential weight-related health risks.
Worked Example
A person who is 5'9" (175 cm) and weighs 170 lbs (77 kg): BMI = 77 ÷ (1.75)² = 77 ÷ 3.0625 = 25.1. This falls in the 'Overweight' range by a narrow margin. To reach the top of the 'Normal' range (BMI 24.9), this person would need to weigh approximately 168 lbs (76.2 kg) — a difference of just 1.8 lbs.
BMI Classification (WHO Standard)
| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Nutritional deficiency, osteoporosis |
| 18.5 – 24.9 | Normal weight | Lowest risk |
| 25.0 – 29.9 | Overweight | Moderate risk of heart disease, diabetes |
| 30.0 – 34.9 | Obese (Class I) | High risk |
| 35.0 – 39.9 | Obese (Class II) | Very high risk |
| 40.0 and above | Obese (Class III) | Extremely high risk |
What is BMI and how is it calculated?
Body Mass Index (BMI) is a screening tool that estimates body fat based on height and weight. It was developed by Belgian mathematician Adolphe Quetelet in the 1830s and is still the most widely used population-level health metric today. BMI is calculated by dividing your weight in kilograms by the square of your height in metres: BMI = kg / m². In imperial units the formula becomes weight (lbs) × 703 ÷ height (inches)².
Worked example: A person who weighs 75 kg and is 1.75 m tall has a BMI of 75 ÷ (1.75 × 1.75) = 75 ÷ 3.0625 ≈ 24.5 — squarely in the "Normal weight" range.
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Normal weight |
| 25.0 – 29.9 | Overweight |
| 30.0 and above | Obese |
Note: BMI is a screening tool, not a diagnostic measure. It does not account for muscle mass, bone density, or fat distribution. Consult a healthcare professional for a full assessment.
How to Use
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Use the Bmi Calculator tool above.
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