BMI is a useful screening tool but has limitations. It does not account for muscle mass, bone density, age or sex differences. Athletes may have a high BMI despite being very healthy.

⚖️ BMI Calculator – Body Mass Index Calculator

Calculate your Body Mass Index (BMI) instantly. Find out if you are underweight, normal weight, overweight or obese. Supports metric units (kg and cm) and imperial units (lbs and inches). Free, fast and accurate.

BMI Calculator — Body Mass Index

Enter your height and weight to calculate your BMI instantly

Units

Weight

Height

—

Healthy BMI Range

18.5 – 24.9 kg/m²

for adults

BMI Prime

—

ratio to upper normal

⚖️ Healthy Weight Range for Your Height

Underweight (BMI <18.5) —

Normal weight (BMI 18.5–24.9) —

Overweight (BMI 25–29.9) —

Obese (BMI ≥30) —

To Reach Normal (lower)

—

To Reach Normal (upper)

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What is BMI? Body Mass Index Explained

BMI (Body Mass Index) is a measurement that uses your height and weight to estimate whether your body weight is healthy. It is calculated by dividing your weight in kilograms by the square of your height in metres.

Formula: BMI = weight (kg) ÷ height² (m²)

For example, a person who weighs 70kg and is 1.75m tall has a BMI of 70 ÷ (1.75 × 1.75) = 22.9 — which is in the normal range.

BMI Categories and Healthy Weight Ranges

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

Limitations of BMI

BMI is a useful screening tool but has important limitations:

Athletes and bodybuilders may have a high BMI due to muscle mass, not fat
Elderly people may have a normal BMI despite excess body fat due to muscle loss
Different ethnicities may have different health risks at the same BMI
BMI does not measure body fat distribution — where fat is stored matters too

Always consult a healthcare professional for a complete health assessment.

BMI Calculator – Metric and Imperial Units

Our free BMI calculator works for adults worldwide. Whether you measure in kilograms and centimetres (used in the UK, Australia, Canada, India and most of the world) or pounds and inches (used in the United States), simply select your preferred unit and enter your details.

BMI — also called the body mass index — is used by doctors, nurses, dietitians and health professionals globally as a quick screening tool for weight-related health risks. While BMI does not directly measure body fat, research consistently shows it correlates with more direct measures of body fat for most adults.

BMI Formula

The BMI formula differs slightly depending on which units you use:

Metric: BMI = weight (kg) ÷ height² (m²)
Imperial: BMI = 703 × weight (lbs) ÷ height² (inches²)

Who Should Use a BMI Calculator?

BMI calculators are useful for adults aged 18 and over. They are used for routine health checks, insurance assessments, medical screenings and personal fitness tracking. Note that BMI is not recommended as a standalone measure for children, pregnant women, athletes or elderly individuals, as body composition varies significantly in these groups.

Frequently Asked Questions

What is a healthy BMI for adults? +

For most adults, a BMI between 18.5 and 24.9 is considered healthy. However, the ideal range may vary slightly by age, sex and ethnicity. Asian populations, for example, may face health risks at lower BMI thresholds (23+).

Is BMI accurate for children? +

BMI for children and teenagers is calculated the same way but interpreted differently using age and sex-specific percentile charts. The adult BMI categories do not apply to children. Consult a paediatrician for child BMI interpretation.

What is BMI Prime? +

BMI Prime is your BMI divided by 25 (the upper limit of normal). A BMI Prime of 1.0 means you are exactly at the upper edge of normal. Below 1.0 is normal or underweight, above 1.0 is overweight or obese. It gives a quick sense of how far from normal you are.

How can I lower my BMI? +

To lower your BMI you need to reduce body fat through a combination of a calorie-controlled diet and regular exercise. A deficit of 500 calories per day typically leads to about 0.5kg weight loss per week. Use our Calorie Calculator to find your daily calorie target.

📊 BMI Scale

Underweight< 18.5

Normal18.5 – 24.9

Overweight25 – 29.9

Obese≥ 30

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