How to Use BMI Calculator
- Select Your Preference of Units: Either choose Metric (kg, cm) or Imperial (lbs, feet and inches).
- Enter Your Height & Weight: Type your present height without wearing any footwear along with your exact weight to get an accurate value of your BMI.
- Get Your BMI Calculation Results: Get your calculated BMI value, check in which category you lie according to WHO criteria, and your ideal weight according to your height.
One Tip for More Accuracy: It is recommended that try measuring your weight in the morning before eating anything and going to the toilet.
Explanation & How It Works
The BMI (Body Mass Index) was developed in the nineteenth century by Adolphe Quetelet, who is a Belgian mathematician. This is done by using the ratio of the weight of a person to his or her square height in order to estimate the body mass.
It is important to note that although the body mass index is not a measure of body fat content, it has been proven through epidemiological studies that the BMI correlates highly with actual measures of body fat content (for instance, hydrostatic weighing).
Calculation Formula & Rules
BMI = Weight (kg) / [Height (m)]²Imperial Formula:
BMI = 703 × Weight (lbs) / [Height (inches)]²
BMI Prime:
BMI Prime = Actual BMI / 25 (Values under 0.74 indicate underweight; 0.74–1.00 indicate optimal health; >1.00 indicate overweight).
Example Calculation
Calculation Walkthrough:
For an individual weighing 72 kg with a height of 175 cm (1.75 m):
- Height squared = 1.75 × 1.75 = 3.0625 m²
- BMI = 72 / 3.0625 = 23.51 kg/m²
- Status: Normal / Healthy Weight (WHO category 18.5 – 24.9).
Official BMI Classification Chart by WHO and CDC
Adult BMI classification according to WHO & CDC standards:
| BMI Range (kg/m²) | Classification | Health Risk |
|---|---|---|
| < 16.0 | Severe Thinness | High risk of nutrient deficiency and osteoporosis |
| 16.0 – 16.9 | Moderate Thinness | Increased nutritional risk |
| 17.0 – 18.4 | Mild Thinness | Moderate risk |
| 18.5 – 24.9 | Normal Weight | Lowest risk of death from all causes |
| 25.0 – 29.9 | Overweight (Pre-obesity) | Increased risk of high blood pressure and diabetes |
| 30.0 – 34.9 | Obese Class I (Moderate) | High risk of heart diseases and metabolic disorders |
| 35.0 – 39.9 | Obese Class II (Severe) | Very high risk of diseases |
| ≥ 40.0 | Obese Class III (Morbid) | High risk / surgery required zone |
BMI Limitations: Importance of Lean Mass
BMI is not a diagnostic tool, but a screening one. BMI doesn't account for fat mass vs lean mass of a person. Thus, highly developed athletes, bodybuilders and other physically fit individuals may get their BMI classified as "overweight" or "obese" even if their body fat and cardiovascular fitness are at their best. For a detailed analysis, use BMI together with our Body Fat Calculator and Waist to Height Ratio calculator.