Body Mass Index Calculator

Introduction to the body mass index (BMI)

The WHO (World Health Organization) has developed different BMI (Body Mass Index) classification standards based on different age groups and genders. The following are the common BMI classification standards of WHO (the details of the classification vary according to age and gender)

• BMI categories for adults (18 years and older)

  For adults, the BMI classification standards are unified and do not distinguish between genders, but there can usually be some variations based on age, body fat distribution, etc.

  BMI	Classification
  < 18.5	Underweight
  18.5 - 24.9	Normal weight
  25 - 29.9	Overweight
  30 - 34.9	Obesity (Class 1)
  35 - 39.9	Obesity (Class 2)
  > 40	Obesity (Class 3)

• BMI categories for children and adolescents (2-19 years)

  For BMI classification of children and adolescents, WHO uses percentile standards based on age and gender. The healthy range of BMI varies according to different age groups. The standards include the following ranges:

  Percentile	Classification
  < 5th	Underweight
  5th - 85th	Normal weight
  85th - 95th	Overweight
  > 95th	Obesity

• Gender differences

  Although the WHO BMI standard does not specifically distinguish between adult genders, the relationship between body fat distribution and BMI may be different for men and women in some special health assessments. Generally speaking, women have higher body fat content than men, which may also affect the assessment of underweight, normal weight, overweight or obesity. However, the WHO standard is generally a unified classification standard applicable to all genders.

What your BMI result means

A BMI range of 18.5 to 24.9 is considered a 'healthy weight.' Maintaining a healthy weight may lower your chances of experiencing health issues later on, such as obesity and type 2 diabetes. Aim for a nutritious diet with reduced fat and sugar content, incorporating ample fruits and vegetables. Additionally, strive for regular physical activity, ideally about 30 minutes daily for five days a week.

How to maintain good physical condition

Limitations of BMI

Although BMI is often a practical indicator of healthy weight, it is not suited for every person. Specific groups should carefully consider their BMI outcomes, and in certain cases, the measurement may not be beneficial to use.

• Gender

  The development and body fat composition of girls and boys vary with age. Consequently, a child's age and gender are considered when evaluating their BMI.

• Age

  In aging individuals, increased body fat and muscle loss may cause BMI to underestimate body fat content.

• Muscle

  BMI may misclassify muscular individuals as overweight or obese, as it doesn't differentiate muscle from fat.

• Pregnancy

  Expectant mothers experience weight gain due to their growing baby. Maintaining a healthy pre-pregnancy BMI is advisable to minimise health risks for both mother and child.

• Race

  Certain health concerns may affect individuals of some Black and Asian origins at lower BMIs than others. To learn more, it is advised to discuss this with your GP or practice nurse.

How to calculate BMI

If you want to calculate your BMI, you have to find out your weight and height first. Once you know these values, you can arrive at the result by following the two steps mentioned below:

• Multiply your height by itself (height X height). For example, if you are 1.75 meters tall, you would multiply 1.75 by 1.75 to get 3.0625.
• Divide your weight by the answer you get in the first step.