Free BMI Calculator 2026 β Metric & Imperial
Instantly calculate your Body Mass Index with WHO health zones, ideal weight range, and personalized health advice. Supports metric (kg/cm) and imperial (lbs/ft/in). No sign-up. Free forever.
Weight
Weight
Ideal
WHO BMI Classification
| Category | BMI Range | Health Risk | |
|---|---|---|---|
| Underweight | < 18.5 | Increased | |
| Normal Weight | 18.5 β 24.9 | Minimal | |
| Overweight | 25.0 β 29.9 | Increased | |
| Obese Class I | 30.0 β 34.9 | High | |
| Obese Class II | 35.0 β 39.9 | Very High | |
| Obese Class III | β₯ 40.0 | Extremely High |
What Is BMI and How Is It Calculated? β Complete Guide 2026
Body Mass Index (BMI) is a widely used screening tool that estimates whether a person has a healthy body weight relative to their height. Developed by Belgian mathematician Adolphe Quetelet in the 19th century, it was adopted by the World Health Organization (WHO) as a global standard for classifying weight status in adults.
Our free BMI calculator supports both metric units (kilograms and centimetres) used in the UK, Europe, Canada, Australia and most of the world, as well as imperial units (pounds, feet and inches) preferred in the United States and a few other countries.
BMI Formula β Metric and Imperial
Metric formula: BMI = weight (kg) Γ· heightΒ² (mΒ²)
Example: 70 kg Γ· (1.75 m)Β² = 22.9 β Normal weight
Imperial formula: BMI = (weight in lbs Γ 703) Γ· heightΒ² (inchesΒ²)
Example: (154 lbs Γ 703) Γ· (69 in)Β² = 22.7 β Normal weight
WHO BMI Classification for Adults
The World Health Organization defines the following BMI categories for adults aged 18 and over:
- Underweight: BMI below 18.5 β risk of nutritional deficiency, osteoporosis, anaemia
- Normal weight: BMI 18.5 β 24.9 β lowest health risk; target range for most adults
- Overweight: BMI 25.0 β 29.9 β increased risk of cardiovascular disease, type 2 diabetes
- Obese Class I: BMI 30.0 β 34.9 β high risk of metabolic syndrome, hypertension
- Obese Class II: BMI 35.0 β 39.9 β very high risk; serious comorbidities likely
- Obese Class III: BMI 40+ β extremely high risk; medical intervention typically required
BMI for Men vs Women β Key Differences
BMI uses the same formula for all genders, but health professionals note that women naturally carry 10β15% more body fat than men at the same BMI due to hormonal and reproductive differences. A woman with a BMI of 22 and a man with BMI 22 may have meaningfully different health profiles. Some researchers suggest separate BMI thresholds for women or the use of additional metrics such as waist-to-hip ratio.
BMI Limitations β What BMI Doesn't Tell You
BMI is a population-level screening tool, not a personal diagnostic. Its key limitations include:
- Does not distinguish fat from muscle β athletes often have "overweight" BMIs despite low body fat
- Does not measure fat distribution β visceral (belly) fat is more harmful than subcutaneous fat
- Applies differently across ethnic groups β Asian populations show higher metabolic risk at lower BMI thresholds (overweight β₯ 23, obese β₯ 27.5 per WHO Asian standards)
- Not valid for children β use CDC or WHO growth charts with age-sex percentiles
- May be inaccurate for pregnant women, the elderly, or highly muscular individuals
For a fuller picture, combine BMI with waist circumference (health risk increases at >94 cm/37 in for men and >80 cm/31.5 in for women), body fat percentage, blood pressure, and cholesterol levels.
Who Uses This BMI Calculator?
Our free online BMI calculator is used by millions of people in the United States, United Kingdom, Canada, Australia, Germany, Netherlands, Singapore, UAE and 150+ countries. It's used by individuals tracking personal health, healthcare students, fitness coaches, nurses completing patient assessments, and anyone curious about their weight status β all completely free with no account required.