BMI Calculator: Check your body mass index

Looking for a quick, clinically recognized way to assess whether your weight is in a healthy range for your height? Our free BMI calculator uses the standard World Health Organization (WHO) formula to calculate your body mass index in seconds and shows which of the four recognized BMI categories your result falls into.

Calculate your BMI

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Gender: *

Note: The adult BMI mathematical formula is the same for both, but biological fat distribution differs.

This calculator is for adults aged 18 yrs and over. BMI ranges are interpreted differently for children and teens.

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Your total current body weight.

*Estimates only. See full clinical & legal disclaimer below.

What is BMI (Body Mass Index)?

Body mass index (BMI) is a simple, widely used clinical screening tool that compares your weight to your height. It is calculated by dividing your weight in kilograms by your height in meters squared ( kg/m ²).

This calculator doesn’t measure body fat directly. But doctors worldwide still use BMI as a quick, low-cost health screening tool. A GP may use BMI as one part of a more general health assessment, together with waist circumference, blood pressure, blood test results, personal medical history, and lifestyle.

Understanding your BMI results (The clinical ranges)

Your result is measured against four official World Health Organization (WHO) adult BMI classifications. Each category reflects a different level of long-term health risk, not a diagnosis:
Category BMI Range What It May Indicate
Underweight Under 18.5 Possible malnutrition, disordered eating, or another underlying health issue; can affect bone density and immunity
Healthy weight 18.5-24.9 For many adults, this range is associated with a lower risk of some weight-related health problems, but BMI does not measure overall health.
Overweight 25.0-29.9 May be associated with an increased risk of cardiovascular disease, joint issues, and elevated cholesterol depending on the person’s overall health and risk factors
Obese 30.0 and above Higher risk of type 2 diabetes, heart disease, hypertension, and sleep apnea
It’s important to remember that a BMI calculator is a screening tool, not a medical diagnosis. If your BMI is outside the healthy range, a doctor can help you understand what it means for your individual health, lifestyle, and medical history.

Is there a specific BMI calculator for women and men?

The BMI formula is the same for all adults. It relies only on your weight and height ( kg/m ²) and doesn’t include biological sex in the calculation.

While many people often search for a BMI calculator for women, the formula is identical for both sexes. The difference lies in the body composition rather than the calculation itself. Women usually have a higher proportion of essential body fat to support normal reproductive function, whereas men tend to have more muscle mass for the same height and weight.

This means a woman and a man with the same BMI of 25 can have very different physical body compositions. BMI doesn’t measure muscle mass, body fat percentage, or fat distribution; it simply estimates weight relative to height.

The 4 major flaws of the BMI calculator

BMI is a useful screening tool, but it has its limitations. The following groups may find that a standard BMI calculator doesn’t accurately reflect their individual circumstances.

  • Athletes and weightlifters: Muscle is denser than fat, so a heavily muscled rugby player might have a BMI of 31 (categorised as “obese”) while having extremely low body fat and excellent metabolic health. Other measures are needed to assess their health risk.
  • The elderly: Older adults naturally lose muscle mass over time. A “healthy” BMI reading in a 75-year-old can sometimes mask underlying muscle loss, known as sarcopenia, so strength, function, and nutrition may also need assessment.
  • Pregnant Women: BMI isn’t a valid measure during pregnancy because it includes the weight of the baby, placenta, and increased blood volume. A GP, midwife, or obstetrician should be consulted about healthy weight gain during pregnancy.
  • Specific Ethnicities: Research shows that people of Asian, Aboriginal, or Torres Strait Islander descent may face high risks for type 2 diabetes at a lower BMI than the standard cut-offs suggest. As a result, some clinical guidelines recommend considering health risks from a BMI of around 23.0 rather than waiting until 25.

Limitations of BMI

Beyond these groups, BMI has important limitations. It evaluates weight relative to height but cannot distinguish among muscle, fat, bone, and fluid. It doesn’t account for fat distribution, even though abdominal fat is more strongly linked to metabolic health risks than fat stored elsewhere in the body.

For a more thorough assessment, BMI is often combined with other health checks, such as waist circumference, blood pressure, and relevant blood tests. Considering these measures together provides a clearer picture of your overall health.

BMI FAQs

Is BMI accurate for adults?

BMI is a useful screening tool for most adults, but it doesn’t provide a complete picture. It doesn’t take into account muscle mass, bone density, or fat distribution. Hence, it works best alongside other health checks to provide a more complete assessment.
The healthy BMI range for adult women is the same as for men: 18.5 to 24.9. The BMI equation doesn’t change based on biological sex. However, women generally have a higher proportion of essential body fat than men with the same BMI.
Divide your weight in kilograms by your height in meters, then divide that result by your height in meters again (weight ÷ height²). For example, someone weighing 70kg at 1.70m would calculate 70 ÷ (1.70 x 1.70) = 24.2.
For some people of Asian descent, some medical guidelines use a lower BMI threshold of around 23 rather than 25. This is because they have a higher risk of diabetes and heart disease at lower BMI levels.
Being overweight can increase the risk of conditions such as cardiovascular disease, type 2 diabetes, high cholesterol, and joint problems. However, everyone’s risk is different and depends on factors such as diet, exercise, and family history.
No single measurement is perfect, but waist circumference, waist-to-hip ratio, and body fat percentage can offer additional context that BMI misses. Many doctors use these measures alongside BMI to provide a more comprehensive assessment of your health.
Being underweight can be associated with malnutrition, a weakened immune system, reduced bone density, and fertility issues. It can also be a sign of an underlying health condition or eating disorder.
dr-nelson-lau

Medically reviewed by

MBBS, FRACGP, General Practitioner, 30+ Years of Experience

General medical disclaimer: Estimates only. This BMI calculator uses standard World Health Organization (WHO) formulas to provide a general screening metric based on height and weight. It does not measure body fat percentage and cannot account for muscle mass, bone density, age, or ethnicity. A high BMI is an indicator of potential health risks, not a definitive medical diagnosis. This tool does not provide medical advice. Always consult a registered GP or healthcare professional for a comprehensive evaluation of your metabolic health and weight. This adult calculator is not designed to interpret BMI for children or teenagers.

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