Free online BMI (Body Mass Index) calculator. Enter your weight and height to get your BMI and your WHO classification: underweight, normal, overweight or obesity.
What BMI is and how it's calculated
BMI (Body Mass Index, also known as IMC in Spanish) is an indicator that relates your weight to your height to classify your nutritional status. The World Health Organization (WHO) has used it since 1985 as a fast, cheap population-screening tool.
This BMI calculator is free, online, and requires no signup. You only need your weight (in kg) and your height (in cm). The result tells you whether you're underweight, normal weight, overweight or obese per the official WHO ranges. Important: BMI is a screening tool, not a diagnosis — it doesn't distinguish muscle mass from fat, so an athlete can read 'overweight' without actually having excess fat. For a more complete assessment, combine the result with the body composition calculator.
WHO scale
Your BMI: 24.5
- Underweight
- Normal weight
- Overweight
- Obesity grade I
- Obesity grade II
- Obesity grade III
Body Mass Index is a simple formula (weight in kg divided by height in metres squared) that the WHO uses as a population-screening tool to classify normal weight, overweight and obesity.
When it's useful
For large-scale epidemiological studies and as a first filter in clinic. It's fast, requires no device and correlates reasonably with the risk of cardiometabolic disease in average sedentary populations.
Its limitations
It doesn't distinguish between muscle mass and fat mass. A bodybuilder at 90 kg and 1.75 m can read BMI 29.4 (overweight) with 8% body fat. An older person with sarcopenia can read BMI 22 (normal) with 35% body fat. For individual decisions, combine BMI with circumferences (waist) and body composition.
Frequently asked questions
Is BMI reliable?+
It's a quick screening tool for the general population, but it has important limitations: it doesn't distinguish muscle from fat. An athlete can read 'overweight' without excess fat. For more precision, use methods like bioimpedance or the Navy method.
How do I interpret the result?+
<18.5 underweight; 18.5-24.9 normal; 25-29.9 overweight; 30-34.9 obesity I; 35-39.9 obesity II; ≥40 obesity III. But contextualise with body composition and habits.