BMI Quick Reference
Body Mass Index (BMI) is a screening measure of body weight relative to height. It is calculated as weight in kilograms divided by the square of height in meters, or using the imperial formula (weight in pounds × 703) ÷ height in inches squared.
- Normal BMI range (WHO)
- 18.5 – 24.9
- Overweight threshold
- 25.0
- Obese threshold
- 30.0
- Metric formula
- BMI = weight (kg) ÷ height (m)²
- Imperial formula
- BMI = (weight in lbs × 703) ÷ height (in)²
- Adult calculator
- Ages 18+
- Cost
- Free, no account required
Metric formula
BMI = weight (kg) ÷ height (m)²
Example: 70 kg at 175 cm → BMI 22.9 (70 ÷ (1.75)² = 22.9)
Imperial formula
BMI = (weight in lbs × 703) ÷ height (in)²
Example: 154 lbs at 5 ft 9 in → BMI 22.7 ((154 × 703) ÷ (69)² = 22.7)
WHO BMI categories
| BMI range | Category | Health risk |
|---|---|---|
| Below 18.5 | Underweight | Increased risk of malnutrition and osteoporosis |
| 18.5 – 24.9 | Normal weight | Lowest health risk |
| 25.0 – 29.9 | Overweight | Moderate increased health risk |
| 30.0 – 34.9 | Obese Class I | High increased health risk |
| 35.0 – 39.9 | Obese Class II | Very high increased health risk |
| 40.0 and above | Obese Class III | Extremely high increased health risk |
Last updated: 20 July 2026. Use the BMI calculator above for instant results.
What Is Body Mass Index (BMI)?
Body Mass Index (BMI) is a widely used screening tool that estimates body fat based on your height and weight. Developed in the 19th century by Belgian mathematician Adolphe Quetelet, BMI provides a simple numeric measure that healthcare professionals use to categorize weight status and identify potential health risks.
While BMI does not directly measure body fat percentage, research shows it correlates reasonably well with more precise methods like dual-energy X-ray absorptiometry (DEXA) scans for most of the general population.
Limitations of BMI
BMI is a useful population-level screening tool, but it has important limitations for individuals:
- Athletes and muscular individuals may have a high BMI due to muscle mass rather than excess fat.
- Older adults may have a "normal" BMI while carrying excess body fat and losing muscle mass.
- Ethnic differences — some populations face elevated health risks at lower BMI thresholds.
- Does not account for fat distribution, bone density, or overall body composition.
Always consult a qualified healthcare provider for a comprehensive health assessment.
Sources & References
BMI categories and guidance on this page align with standards from leading health organizations:
- World Health Organization (WHO) — BMI classification
- Centers for Disease Control and Prevention (CDC) — About adult BMI
- National Institutes of Health (NIH) — Calculate your BMI
Frequently Asked Questions
What is BMI?
Body Mass Index (BMI) is a measure of body weight relative to height. It is calculated as weight in kilograms divided by the square of height in meters, or as (weight in pounds × 703) ÷ height in inches squared.
How do I calculate my BMI?
Metric: BMI = weight (kg) ÷ height (m)². Imperial: BMI = (weight in lbs × 703) ÷ height (in)². Example: a person who is 175 cm and 70 kg has BMI 22.9 (normal weight).
What is a healthy BMI for adults?
According to the World Health Organization, a normal BMI for adults is 18.5 to 24.9. Below 18.5 is underweight, 25.0–29.9 is overweight, and 30.0 or above is obese.
What BMI is considered obese?
A BMI of 30.0 or higher is classified as obese by the WHO: Class I (30.0–34.9), Class II (35.0–39.9), and Class III (40.0 and above).
How do I calculate BMI for 175 cm and 70 kg?
Convert 175 cm to 1.75 m. BMI = 70 ÷ (1.75)² = 70 ÷ 3.0625 = 22.9. This falls in the normal weight range (18.5–24.9).
Is BMI accurate for athletes and muscular people?
BMI may overestimate body fat in muscular individuals because it does not distinguish muscle from fat. Athletes and people with high muscle mass should use additional measures such as body composition analysis.
Can I use this BMI calculator for children?
No. BMI for children and teens uses age- and sex-specific percentile charts. This calculator is intended for adults aged 18 and older.
Is BMI the same as body fat percentage?
No. BMI is a weight-for-height index. Body fat percentage directly measures fat mass. A muscular person can have a high BMI but low body fat.
Is there a free online BMI calculator?
This site offers a free, accurate BMI calculator supporting metric and imperial units with instant WHO category results. No account required.