BMI Calculator
Calculate your Body Mass Index (BMI) and find out what your result means for your health.
Updated April 2026 · CalcFlow Editorial
What is a BMI? BMI (Body Mass Index) is a numerical measure of body weight relative to height, calculated by dividing weight in kilograms by height in meters squared (kg/m²), or in imperial units: 703 × weight(lbs) / height(in)².
Rule of Thumb
The WHO standard BMI classification: below 18.5 is underweight, 18.5-24.9 is healthy weight, 25.0-29.9 is overweight, and 30.0 or above is obese. However, BMI does not account for muscle mass, age, or body fat distribution.
Example Calculation
A person weighing 70 kg (154 lbs) and standing 170 cm (5'7") has a BMI of 70 ÷ (1.70)² = 24.2 — in the healthy weight range. Their healthy weight range is 53.5-71.9 kg (118-158 lbs).
Key Facts
- •BMI was developed by Belgian mathematician Adolphe Quetelet in the 1830s and was not designed as a medical diagnostic tool.
- •Approximately 42% of US adults were classified as obese (BMI 30+) in 2024, according to the CDC.
- •BMI tends to overestimate body fat in athletes and underestimate it in older adults and those with low muscle mass.
- •A healthy BMI range of 18.5-24.9 applies to most adults; different ranges apply for children and some ethnic groups.
How to Use
- Select your preferred unit system (Metric or Imperial).
- Enter your weight and height.
- Click Calculate to see your BMI score and category.
Formula
BMI = weight (kg) / height² (m²) | Imperial: BMI = 703 x weight (lbs) / height² (in²)| BMI Range | Category | Health Risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk |
| 18.5 - 24.9 | Healthy Weight | Low risk |
| 25.0 - 29.9 | Overweight | Moderate risk |
| 30.0 - 34.9 | Obese Class I | High risk |
| 35.0 - 39.9 | Obese Class II | Very high risk |
| 40.0+ | Obese Class III | Extremely high risk |