BMI Calculator BMI BMI Calculator

Calculate your Body Mass Index (BMI) and discover how you compare to the US population for your age and gender.

Everything about BMI (Body Mass Index)

What is BMI?

Body Mass Index (BMI) is a simple indicator that allows you to quickly assess whether your weight is appropriate for your height. It is calculated using the formula:

BMI = Weight (kg) / Height² (m²)

For example, if you weigh 70 kg and are 1.75 m tall:

BMI = 70 / (1.75 × 1.75) = 70 / 3.06 = 22.9

Note: BMI is a public health indicator, but it does not account for body composition (muscle mass vs fat mass). A very muscular runner may have a high BMI without being overweight.

BMI interpretation according to WHO

Category BMI (kg/m²) Health risks
Underweight < 18.5 Nutritional deficiencies, fatigue, weakened immune system
Normal weight 18.5 – 24.9 Minimal health risks
Overweight 25.0 – 29.9 Increased risk of cardiovascular disease and diabetes
Moderate obesity (Class I) 30.0 – 34.9 High risk
Severe obesity (Class II) 35.0 – 39.9 Very high risk
Massive obesity (Class III) ≥ 40 Extremely high risk

These thresholds are defined by the World Health Organization (WHO) and are valid for adults aged 18 and over.

BMI and running performance

In running, weight plays a crucial role in performance. Here are some benchmarks:

  • Elite runners: BMI typically between 18 and 21 (very light to optimize power-to-weight ratio)
  • Competitive amateur runners: BMI between 20 and 23
  • Recreational runners: BMI between 22 and 26 (healthy and comfortable zone)

Important: A BMI that's too low can lead to injuries, chronic fatigue, and deficiencies. The goal is not to be as light as possible, but to find your optimal racing weight.

BMI limitations

BMI is a practical but imperfect tool. Its main limitations:

  • Does not distinguish muscle from fat: A very muscular bodybuilder will have an "overweight" BMI despite having little body fat
  • Does not account for fat distribution: Abdominal (visceral) fat is more dangerous than subcutaneous fat
  • Varies by age and ethnicity: Thresholds may differ for Asian populations, for example
  • Not suitable for athletes: Athletes often have more muscle mass, which skews the interpretation

For a more precise assessment, you can measure your waist circumference, your body fat percentage (using a bioimpedance scale or skinfold caliper), or consult a health professional.

How to improve your BMI for running?

If your BMI is too high:

  • Favor a balanced diet with a slight caloric deficit (no drastic diets!)
  • Gradually increase your training volume (easy running)
  • Combine running with strength training to preserve muscle mass
  • Aim for gradual weight loss: 0.5 to 1 kg per month maximum

If your BMI is too low:

  • Increase your caloric intake, especially carbohydrates and proteins
  • Temporarily reduce training volume if you're overtraining
  • Consult a sports nutritionist to adjust your diet
  • Watch for signs of fatigue, recurring injuries, or amenorrhea (in women)

Advice: The goal is not to reach a specific number, but to feel good, injury-free, and perform well. Listen to your body above all!

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