BMI Calculator

Calculate your Body Mass Index (BMI) in seconds using metric or imperial measurements.
See your BMI category, understand what your result means, and learn whether your weight falls within a healthy range.

BMI (Body Mass Index) is a screening tool that estimates whether your weight is appropriate for your height. A BMI between 18.5 and 24.9 is generally considered healthy for most adults. Use the calculator below to find your BMI and understand what your result may mean.

What is BMI?

Body Mass Index, or BMI, is a simple calculation that uses your height and weight to estimate whether your weight falls within a healthy range for most adults. It is commonly used by healthcare professionals as a screening tool, but it does not directly measure body fat, muscle mass, fitness, or overall health.

BMI can be useful because weight alone does not show whether someone is underweight, a healthy weight, overweight, or in the obesity range for their height. Your result should be treated as a guide, not a diagnosis, and considered alongside factors such as waist measurement, age, ethnicity, muscle mass, symptoms, and medical history.

BMI Scores for Adults

The World Health Organization (WHO) uses BMI categories to help classify weight ranges in adults aged 20 and over. These categories can indicate whether a person may be underweight, within a healthy weight range, overweight, or living with obesity.

Category BMI Range
Severe Thinness Below 16
Moderate Thinness 16 to less than 17
Mild Thinness 17 to less than 18.5
Normal (Healthy Weight) 18.5 to less than 25
Overweight 25 to less than 30
Obese Class I 30 to less than 35
Obese Class II 35 to less than 40
Obese Class III 40 or greater

Health Risks Outside a Healthy BMI Range

A BMI below or above the healthy range may be linked with a higher risk of certain health problems. The type of risk depends on whether your BMI is low, overweight, or within the obesity range.

A higher BMI may be associated with conditions such as type 2 diabetes, high blood pressure, high cholesterol, heart disease, sleep apnoea, osteoarthritis, and some types of cancer.

A low BMI may be associated with malnutrition, vitamin or mineral deficiencies, weakened immunity, fatigue, hormonal changes, or underlying medical conditions.

  • Diabetes
  • High blood pressure
  • Heart disease
  • High cholesterol
  • Sleep apnea
  • Osteoarthritis
  • Some types of cancer
  • Malnutrition

BMI alone cannot determine whether you are healthy or diagnose a medical condition. If your weight has changed unexpectedly, your BMI falls outside the healthy range, or you have symptoms that concern you, it may be worth speaking to a doctor for personalised advice.

The Limits of BMI

BMI provides more context than scale weight alone, but it has important limitations. It does not directly measure body fat, muscle mass, bone density, fitness, or how fat is distributed around the body. This means two people with the same BMI may have very different health profiles.

Athletes, weightlifters, and people with higher muscle mass may have a higher BMI without having excess body fat. BMI may also be less reliable for older adults, pregnant women, people under 18, people with a condition affecting height, and anyone with or recovering from an eating disorder.

BMI is best used as a screening tool, not a diagnosis. Your result should be interpreted alongside other factors such as waist measurement, symptoms, medical history, blood pressure, cholesterol, blood sugar, lifestyle, and family history.

Medically reviewed

Dr. Chrysoula I. Liakou MD, PhD Google Scholar LinkedIn

Internal Medicine Specialist
Cancer Immunology Researcher

Frequently Asked Questions About BMI

For most adults, a BMI from 18.5 to less than 25 is usually considered the healthy weight range. A BMI below 18.5 may indicate underweight, 25 to less than 30 may indicate overweight, and 30 or above falls within the obesity range. BMI is a screening tool, so your result should be interpreted alongside other health factors.

BMI is calculated by dividing weight in kilograms by height in metres squared:

BMI = weight kg ÷ height m²
For example, someone who weighs 70 kg and is 1.75 m tall would have a BMI of 22.9.

Not always. BMI does not distinguish between fat and muscle. Someone with high muscle mass may have a high BMI without having excess body fat.

BMI is usually based on pre-pregnancy weight. If you are pregnant, BMI may not accurately reflect your current health or body composition, so it is better to speak to a healthcare professional.

You should consider speaking to a doctor if your BMI is below 18.5, 30 or above, changing unexpectedly, or if you have symptoms such as fatigue, breathlessness, unplanned weight loss, swelling, chest pain, or concerns about eating patterns.

Questions about your weight or health?

If you are concerned about your BMI, struggling to gain or lose weight, or have noticed unexpected changes in your weight, speaking to a doctor can help. A consultation can identify potential underlying causes, assess your overall health, and provide personalised advice based on your individual circumstances.

Speak to a licensed doctor online from the comfort of your home and get personalised medical advice in minutes.

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