How is BMI calculated?

BMI = weight (kg) divided by height (m) squared.

BMI Calculator — Free, Metric & Imperial

Q: What is a healthy BMI range?

A healthy BMI for adults is between 18.5 and 24.9 according to the WHO.

Q: Is BMI accurate for muscular people?

BMI does not distinguish muscle from fat. Athletes often score as overweight despite low body fat.

Q: What is a healthy BMI for women?

The same WHO range applies: 18.5 to 24.9.

Q: Does BMI change with age?

The formula stays the same, but older adults (65+) may benefit from a slightly higher BMI of 25-27.

Weight

Drag to adjust75 kg

Height

Drag to adjust175 cm

Your BMI

24.5

Normal weight

Healthy BMI range: 18.5 – 24.9

58.4 kgMin healthy

66.4 kgIdeal midpoint

76.4 kgMax healthy

You're in the healthy range

Ask AI about your result

Thinking…

AI can make mistakes — always verify health information with a qualified professional.

What is BMI (Body Mass Index)?

Body Mass Index is a number calculated from your height and weight that serves as a screening tool for healthy weight ranges in adults. Originally developed by Belgian mathematician Adolphe Quetelet in the 1830s, it was adopted by the World Health Organization (WHO) as a global standard for classifying underweight, normal weight, overweight, and obesity.

BMI is widely used because it is fast, free, and non-invasive. Its limitations — it cannot distinguish muscle from fat, and does not account for where fat is distributed — are well documented, but it remains the most universal first-pass indicator of healthy weight worldwide.

BMI Formula — How It's Calculated

The formula is identical worldwide. This calculator handles all unit conversions automatically.

Metric: BMI = weight (kg) ÷ height (m)²
Example: 75 kg ÷ (1.75 m)² = 75 ÷ 3.0625 = 24.5

Imperial: BMI = (weight lbs × 703) ÷ height (inches)²
Example: (165 lbs × 703) ÷ (69 in)² = 116,000 ÷ 4,761 = 24.4

BMI Classification — WHO Standards

Category	BMI Range	Health Risk
Underweight	Below 18.5	Nutritional risk
Normal weight	18.5 – 24.9	Minimal risk
Overweight	25.0 – 29.9	Increased risk
Obese class I	30.0 – 34.9	High risk
Obese class II	35.0 – 39.9	Very high risk
Severely obese	40.0 and above	Extremely high risk

BMI Guidelines Around the World

🇺🇸

United States

CDC uses WHO ranges. Asian-Americans may be screened at BMI ≥23 due to higher metabolic risk.

🇬🇧

United Kingdom

NHS uses standard WHO ranges with adjusted thresholds for Black, Asian and minority ethnic groups.

🇨🇦

Canada

Health Canada follows WHO. Waist circumference recommended alongside BMI for adults BMI 18.5–34.9.

🇦🇺

Australia

Government and Heart Foundation use WHO ranges with adjusted thresholds for First Nations peoples.

🇮🇳

India / South Asia

Lower cutoffs: overweight ≥23, obese ≥27.5. Metabolic risk increases at lower BMI in South Asian populations.

🇩🇪

Germany / Europe

European agencies follow WHO. German clinical guidelines add waist-to-height ratio as an additional predictor.

Limitations of BMI

Doesn't measure body fat directly. A muscular athlete and a sedentary person of the same height and weight have the same BMI despite very different body compositions.
Ignores fat distribution. Visceral fat (abdomen) is far more dangerous than subcutaneous fat, but BMI cannot see the difference.
Age and sex differences. Women naturally carry more body fat than men at the same BMI. Older adults lose muscle mass, skewing results.
Ethnic variation. People of Asian descent carry greater metabolic risk at lower BMI values. Some countries use adjusted cutoffs.

Frequently Asked Questions

What is a healthy BMI range? ↓

A healthy BMI for adults is 18.5 to 24.9 kg/m² according to the WHO. Below 18.5 is underweight, 25–29.9 is overweight, and 30 or above falls into obesity categories.

Is a BMI of 25 overweight? ↓

Yes — a BMI of 25.0 sits at the lower boundary of the overweight classification. Many organisations consider 18.5–25.0 healthy, so 25.0 is borderline. Other factors like waist circumference provide a fuller picture.

What is a good BMI for a woman? ↓

The same WHO range applies: 18.5 to 24.9. Research suggests post-menopausal women over 50 may benefit from a slightly higher BMI (up to 27) for bone density.

Is BMI accurate for muscular people? ↓

BMI is not accurate for highly muscular individuals. Athletes often register as overweight despite very low body fat. A DEXA scan or body fat measurement is more meaningful for athletic individuals.

How do I calculate BMI in stones and feet? ↓

Use the stone and ft/in tabs in the calculator above — it converts automatically. Manually: multiply stone by 6.35029 to get kg, convert height to metres, then apply BMI = kg ÷ m².

Does BMI change with age? ↓

The formula doesn't change, but for adults 65 and older, a BMI of 25–27 may actually be protective — associated with better survival and lower frailty due to age-related muscle loss.

What health risks are linked to high BMI? ↓

A BMI of 30+ is associated with significantly increased risk of type 2 diabetes, heart disease, stroke, sleep apnoea, and several cancers. Even a 5–10% weight loss meaningfully reduces these risks.

What should I do if my BMI is outside the healthy range? ↓

BMI is a screening tool, not a diagnosis. Speak with your doctor or a registered dietitian for a full, personalised assessment. Small, sustainable changes are more effective long-term than crash diets.

Related Health Calculators

Last updated: March 2026

⚕️ Medical disclaimer: This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. BMI classifications are based on WHO guidelines. Always consult a qualified healthcare professional before making changes to your diet, exercise, or health routine.