BMI (Body Mass Index) is a simple calculation using height and weight to estimate whether a person has a healthy weight for their height. Despite its limitations, it remains one of the most widely used screening tools in healthcare worldwide.
The BMI Formula
Metric: BMI = weight (kg) ÷ height (m)²
Imperial: BMI = [weight (lbs) ÷ height (inches)²] × 703
Imperial example: Weight = 165 lbs, Height = 69 inches (5'9"). BMI = [165 ÷ (69 × 69)] × 703 = [165 ÷ 4,761] × 703 = 0.03466 × 703 = 24.4 (Healthy weight)
BMI Categories (Adults)
| BMI Range | Category |
|---|---|
| Below 18.5 | Underweight |
| 18.5 – 24.9 | Healthy weight |
| 25.0 – 29.9 | Overweight |
| 30.0 – 34.9 | Obese (Class I) |
| 35.0 – 39.9 | Obese (Class II) |
| 40.0 and above | Severely obese (Class III) |
Healthy Weight Range by Height
| Height | Healthy Weight (BMI 18.5–24.9) |
|---|---|
| 5'0" / 152 cm | 43–57 kg / 95–128 lbs |
| 5'4" / 163 cm | 49–65 kg / 108–145 lbs |
| 5'7" / 170 cm | 53–72 kg / 118–159 lbs |
| 5'10" / 178 cm | 58–79 kg / 129–173 lbs |
| 6'0" / 183 cm | 62–85 kg / 136–186 lbs |
| 6'2" / 188 cm | 65–89 kg / 144–196 lbs |
Asian BMI Categories
The World Health Organization and many health authorities use lower BMI thresholds for people of South Asian, East Asian and Southeast Asian descent. Studies show these populations carry higher health risks at lower BMI values:
- Healthy weight: 18.5–22.9
- Overweight: 23.0–27.4
- Obese: 27.5 and above
Limitations of BMI
BMI has several well-documented limitations that healthcare professionals are aware of:
- Doesn't distinguish fat from muscle: A highly muscular athlete may have a BMI in the "obese" range despite very low body fat.
- Doesn't indicate fat distribution: Central (abdominal) fat is more dangerous than fat elsewhere. Waist circumference is often a better indicator of metabolic risk.
- Age and sex differences: Older adults with the same BMI as younger adults tend to have more body fat. Women naturally carry more fat than men at the same BMI.
- Ethnic variations: As noted above, health risk thresholds differ by ethnicity.
BMI vs Body Fat Percentage
Body fat percentage (measured via DEXA scan, hydrostatic weighing, or the Navy circumference method) is a more direct measure of body composition than BMI. It tells you what proportion of your weight is fat tissue vs lean tissue. However, it requires either specialized equipment or additional measurements. Use our Body Fat Calculator to estimate your percentage from simple measurements.
Calculate your BMI instantly and see your healthy weight range.
Use the BMI Calculator →BMI is a useful screening tool but is one piece of a larger health picture. A healthcare provider uses BMI alongside other factors — waist circumference, blood pressure, cholesterol, blood sugar, physical activity and family history — to assess overall health risk.