What is BMI?

There are lots of ways to determine how healthy a person is, usually taking into account various measurements and physical attributes. BMI is one of the most widely used methods, being understandable for people at any stage of their fitness journey. 

A person's feet on a set of scales.

In this post, we'll be telling you what BMI is, how you can calculate yours, and what the different values can mean for you and your fitness routine.

What is BMI?

BMI stands for 'Body Mass Index'. It uses your height and weight to calculate where you are on a scale, with the ideal BMI for most adults being in the range of 18.5 to 24.9. 

The full list of BMI ranges and their associated weights are as follows: 

Below 18.5 – underweight
Between 18.5 and 24.9 –  healthy weight
Between 25 and 29.9 –  overweight
Between 30 and 39.9 – obese

Why is BMI important?

BMI is seen as important due to the fact that a healthy BMI tends to lead to a longer and healthier life. On the other hand, a BMI in the higher ranges gives you an increased chance of type 2 diabetes, heart disease, and hypertension, to name a few. It's also a reliable way to gauge the amount of body fat a person has and is one of the easiest ways for someone to see how much risk is posed by their weight and take preventative action. 

How to Calculate Your BMI 

There are loads of online calculators that will use your weight and height to find out what your BMI is - we recommend this one from the NHS. But if you want to do the maths yourself, the calculation is still easy  - simply divide your weight in kilograms by your height in meters. So, for a 27-year old moderately active man, who’s 6 feet tall and weighs 80 kilograms, his BMI would be 23.8. This would make him a healthy weight.

A quick note - the details needed for calculation are a bit different for under 18s. If you're in that age bracket, online calculators will take your age and gender into account alongside the usual weight and height.

Reminders about BMI 

BMI is good, but it's not always the best way to ascertain if you are a healthy weight. It doesn't take into account things like high muscle percentage - meaning an athletic rugby player could end up being classed as obese. BMI also doesn't factor in ethnicity, pregnancy or old age - all of which can significantly affect your weight.  For example, studies have shown that adults from Asian backgrounds are more likely to have health problems even if they have a BMI level below 25, and body fat tends to rise as people age. 

Additionally, BMI isn’t the only way to measure your health in relation to your weight - you can also use your abdominal circumference, waist-hip ratio, or waist-height ratio (though that does involve a little more work to get right).

Also, decisions about diet and fitness shouldn't be made purely based on BMI. It's not there to make you feel self-conscious, either - but to empower you to take the next steps in weight loss should you choose to, such as going to your GP. It's also worth remembering that people suffering or recovering from an eating disorder should not use BMI to analyse their weight and speak with a medical professional instead. 


So, as we've discussed, BMI has its benefits and drawbacks. However, if you're an average person who wants to get a snapshot of your health and what you might need to do to improve it, you can't get a more convenient method than the body mass index.

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