1. BMI Calculation & Classification (Adults)
Formula: BMI = weight (kg) / [height (m)]²
Classifications:
Underweight: < 18.5
Normal range: 18.5 – 24.9
Overweight: 25 – 29.9
Obesity: ≥ 30
2. “Ideal” or Healthy Weight Range by Height
This range typically corresponds to a BMI of 18.5 to 24.9.
| Height (cm) | Healthy Weight Range (kg) | Mid-Range BMI (~21.7) |
|---|---|---|
| 150 | 42 – 56 | 51 |
| 155 | 45 – 59 | 54 |
| 160 | 47 – 64 | 57 |
| 165 | 50 – 68 | 60 |
| 170 | 53 – 72 | 64 |
| 175 | 56 – 76 | 68 |
| 180 | 59 – 81 | 71 |
| 185 | 63 – 86 | 75 |
| 190 | 67 – 90 | 80 |
3. Crucial Adjustments and Limitations
Your points on adjustments are critical, as BMI is a screening tool, not a diagnostic one.
Age:
20-40 years: The standard BMI range is most applicable. Maintaining a stable weight within this range is ideal.
40-60 years: Sarcopenia (age-related muscle loss) begins. A person may have a “normal” BMI but still have a high body fat percentage (“skinny fat”). Body composition (muscle vs. fat) becomes more important than the number on the scale.
60+ years: A BMI in the upper end of the normal range or even slightly overweight (e.g., 25-27) may be associated with better resilience against illness and frailty. However, waist circumference is a vital check to monitor dangerous abdominal fat.
Other Important Factors BMI Does Not Account For:
Muscle Mass: Athletes with high muscle mass may have a BMI in the “overweight” category without health risks.
Body Frame Size & Fat Distribution: Where you carry fat (apple vs. pear shape) is a key indicator of health risk. Waist circumference (>102 cm for men, >88 cm for women) is a crucial additional measure.
Sex and Ethnicity: Body composition differs, and some populations may have different risk thresholds.
Children and Adolescents: As you noted, BMI-for-age percentiles (using growth charts specific to sex and age) must be used—the adult classifications do not apply.
Practical Summary
For a holistic view of healthy weight:
Calculate your BMI as a starting point.
Measure your Waist Circumference (at the navel level) to assess abdominal fat risk.
Consider your Age and Lifestyle: Focus on maintaining muscle through strength training and a protein-rich diet, especially after 40.
Consult a Healthcare Professional for a personalized assessment, including possible body composition analysis.
Your provided data serves as an excellent general guide, and emphasizing these adjustments helps ensure it is applied safely and effectively.
