What is a healthy BMI range?

The WHO defines a healthy BMI as 18.5 to 24.9 for adults. A BMI below 18.5 is classified as underweight, 25–29.9 as overweight, and 30 or above as obese. These thresholds are population averages and may not apply to all individuals or ethnic groups.

What are the limitations of BMI?

BMI does not distinguish between fat mass and muscle mass — a muscular athlete may be classified as overweight. It also does not account for fat distribution (visceral vs subcutaneous), age, sex, or ethnicity. BMI is a screening tool, not a diagnostic measure. Consult a healthcare professional for a full health assessment.

What is BMI?

Q: What is BMI?

BMI (Body Mass Index) is a value derived from height and weight using the formula: BMI = weight(kg) / height(m)². It is used as a population-level screening measure for weight categories. The standard categories are: Underweight (<18.5), Normal (18.5–24.9), Overweight (25–29.9), and Obese (≥30).

BMI (Body Mass Index) is a number derived from height and weight used as a population-level screening measure for weight categories associated with health risk. It is not a diagnostic tool.

Formula

Metric: BMI = weight (kg) ÷ height (m)²

Imperial: BMI = (weight (lb) × 703) ÷ height (in)²

Example: a person weighing 70 kg at 1.75 m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9.

WHO Categories (Adults)

Underweight — BMI below 18.5
Normal weight — BMI 18.5–24.9
Overweight — BMI 25–29.9
Obese Class I — BMI 30–34.9
Obese Class II — BMI 35–39.9
Obese Class III — BMI 40 and above

Limitations

BMI is a blunt instrument:

Muscle mass — athletes often have high BMI without excess fat
Fat distribution — visceral (abdominal) fat carries more risk than BMI alone indicates
Age and sex — older adults and women typically have more body fat at the same BMI
Ethnicity — some guidelines use lower thresholds (23 for overweight) for Asian populations

BMI is best used as a starting point for conversation with a healthcare professional, not a standalone diagnosis.

Calculate your BMI in metric or imperial units: Open BMI Calculator →

Frequently Asked Questions

Is BMI the same for children?

No. For children and teenagers (aged 2–19), BMI is age- and sex-specific. It is plotted on growth charts as a percentile, not compared to fixed thresholds. A BMI in the 85th–94th percentile is "overweight" for children; 95th percentile and above is "obese".

What is a better measure than BMI?

Waist circumference and waist-to-height ratio are better predictors of metabolic risk because they capture abdominal fat distribution. DEXA scans measure body fat percentage directly but require specialist equipment. For most people, BMI combined with waist circumference gives a reasonable picture.