How to calculate your Body Mass Index (BMI)

Body Mass Index, more generally referred to as BMI, is a measurement approach that is used by medical experts such as General Practitioners, dietitians and exercise physiologists as a quick, starting point to help measure whether someone is underweight, healthy, overweight or obese.

The reading is obtained by performing a simple calculation and provides an objective measurement that takes into account your age as well as height.

Most BMIs will fall in between 18 and 30, where 18 is underweight and 30 is obese.

Calculate your BMI by using the calculator below. Be sure to choose the correct unit system for your measurements.

BMI categories

Now you have your BMI, the next step is to understand what it actually says about your health.

Healthcare practitioners use the following guidelines to understand what the number says about your health and weight status.

Understanding BMI

BMI is a number calculated from your weight and height. It helps categorise people into weight groups like underweight, normal weight, overweight, and obese. The formula is simple: weight in kilograms divided by height in metres squared (kg/m²). This makes BMI an easy tool for assessing weight status across different populations.

The historical context of BMI

BMI was introduced in the early 19th century by Belgian mathematician Adolphe Quetelet. Originally for demographic purposes, it became a health tool to assess chronic disease risk. Despite its widespread use, BMI has faced criticism for its limitations.

Why is a healthy BMI important?

Maintaining a healthy BMI is an indicator for overall health and wellbeing.

Risks associated with unhealthy BMI

An unhealthy BMI, whether underweight or overweight, can lead to serious health issues:

• Chronic diseases: A high BMI increases the risk of type 2 diabetes, stroke, and heart disease, which can lower quality of life and life expectancy.

• Mental health effects: There’s a strong link between BMI and mental health. Obesity can lead to depression and anxiety due to societal stigma and self-esteem issues. Being underweight can also cause mental health struggles, including eating disorders and body image issues.

Benefits of maintaining a healthy BMI

A healthy BMI offers many benefits:

• Increased longevity: People with a healthy BMI tend to live longer, healthier lives.

• Improved quality of life: Maintaining a healthy weight can enhance mobility, energy levels, and participation in physical activities.

What are the limitations of BMI?

While useful, BMI has its limitations.

Body composition differences

BMI doesn’t account for body composition. Muscle weighs more than fat, so muscular individuals might be misclassified as overweight or obese.

Population variability

BMI doesn’t consider age, sex, and ethnicity, which affect body composition and fat distribution.

Cultural differences in body types

Cultural definitions of a healthy body shape vary, leading to different interpretations of BMI results.

Situations where BMI is less accurate

BMI may not be accurate in certain cases:

Pregnancy: Pregnant women shouldn’t rely on BMI as it doesn’t account for the additional weight from pregnancy. 

Age factors: As people age, muscle loss and fat gain can change body composition, which BMI doesn’t reflect. 

Diverse cultural backgrounds: Different body fat distributions in various ethnic groups aren’t accounted for by BMI. 

Alternative measurements of health

Other methods can provide a more comprehensive health assessment:

Waist-to-hip ratio: Measures waist and hip circumference to assess fat distribution, useful for abdominal obesity.

Body fat percentage: Techniques like skinfold calipers and bioelectrical impedance offer a clearer picture of body composition.

Tips for achieving and maintaining a healthy BMI

Balanced diet and nutrition: Eat a diet rich in fruits, vegetables, whole grains, and lean proteins. Watch portion sizes and limit processed foods.

Regular physical activity: Combine aerobic exercises and strength training to boost metabolism and maintain a healthy body composition.

Regular health check-ups: Regular visits to healthcare professionals can help monitor BMI and other health markers.

The bottom line

While BMI is a valuable tool, it’s important to recognise its limitations and consider other factors like body composition and lifestyle. By focusing on a balanced diet, regular exercise, and overall wellness, you can improve your health and reduce the risk of chronic diseases.

Main image: Pexels