BMI: Body Mass Index

BMI graph g11 (9)

The ‘Body Mass Index’ (BMI) is a measure of the human body’s relation to its individual height and mass (weight). The scoring system enables a good indication of whether somebody is underweight, overweight or within normal limits for their body shape and size.

Body mass is quite simple to calculate once height and weight have been recorded as the below formula illustrates:


For example, a 60kg female runner who is 1.7m (170cm) tall would have a BMI score of 20.76.

To identify the zone in which your BMI scores, please refer to the below table or the above graph.



Very severely underweight less than 15
Severely underweight from 15.0 to 16.0
Underweight from 16.0 to 18.5
Normal (healthy weight) from 18.5 to 25
Overweight from 25 to 30
Obese Class I (Moderately obese) from 30 to 35
Obese Class II (Severely obese) from 35 to 40
Obese Class III (Very severely obese) over 40

A skilled personal trainer or fitness instructor may use BMI to assess the ratio of bodyweight and height compared to the normal or desirable level illustrated in the table. The index score has been known to come under debate due to the exclusion of extrinsic factors and certain body types. Various factors may influence the reliability and accuracy of the index and these can affect the ratio scoring of bodyweight and height. Such variables include the level of muscle mass (e.g. bodybuilders) or those who suffer from malnutrition or obesity. The weight excess or deficiency may be accounted for by body fat or other factors such as muscularity which may affect the BMI scoring system. These ranges of BMI values are valid only as statistical categories.

Please feel free to contact the Didsbury (Manchester) G4 Clinic to speak to a member of the health and fitness team for any questions that you may have or if you would like a full health assessment and screening.

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