What is BMI?
BMI stands for Body Mass Index and is a tool used by health professionals to assess whether a person is within a healthy weight range. It’s based on a person’s height and weight, and the result places them into a weight category.
How do you calculate BMI?
To calculate BMI, you take a person’s weight and divide it by their height squared.
Is BMI a valid measurment?
BMI can be useful when looking at large groups of people. Health professionals use it to track trends—such as whether more people are becoming overweight or underweight over time. This helps them understand potential health concerns in different communities.
For individuals, BMI can be a helpful starting point; however, it’s important to recognize that it doesn’t tell the full story about a person’s health. It does not differentiate between muscle, fat, bone mass, or water weight. So, while BMI is a useful tool, it has its limitations.
Ideally, BMI should be used alongside other measurements, such as the waist-to-height ratio, to get a clearer picture of a person’s overall health.
BMI and Children
When it comes to children, BMI is measured differently than in adults. Instead of using a simple number, a child’s BMI is plotted on a centile chart, which compares it to others of the same age, sex, and height. For example, if a child falls in the 67th centile, it means that 67% of the children in the same category had a lower BMI.
In the UK, the National Child Measurement Programme (NCMP) records children’s BMI at different ages, typically in Reception (ages 4–5), Year 6 (ages 10–11), and sometimes Year 8 (ages 12–13). This data informs Public Health England and is part of the government’s efforts to address childhood obesity.
Waist-to-Height ratio
This measurement helps assess how much fat is stored around your belly. It compares your waist size to your height, and you can calculate it at home.
Here’s how:
- Measure Your Waist – Use a tape measure to find the circumference of your waist just above your belly button.
- Measure Your Height – Stand straight and measure your height.
- Calculate the Ratio – Divide your waist measurement by your height measurement using the same units (e.g., centimetres or inches).
A healthy waist-to-height ratio is generally less than 0.5, meaning your waist should be less than half your height.
Conclusion
BMI can be a useful tool for understanding general weight trends, but it doesn’t provide a complete picture of individual health—especially for children. It’s best to combine BMI with other measurements, like the waist-to-height ratio, for a more accurate assessment.
If you’re concerned about your child’s weight or notice consistent changes in their centile ranking, speaking with a GP or school nurse can provide guidance and support.
What matters most is building healthy habits, such as:
- Following the Eatwell Guide – Ensuring a balanced diet with plenty of fruits, vegetables, and healthy proteins.
- Reading Food Labels – Using color-coded “traffic light” labels to make informed food choices.
- Staying Active – Encouraging daily physical activity through sports, outdoor play, or family walks.
- Prioritising Sleep – Maintaining a good sleep routine, as rest is essential for both physical and mental health.
The best thing you can do is take care of yourself and enjoy being active every day!