Body Mass Index (BMI)

Body Mass Index compares a person's mass to their height squared, so it gives a simple way to judge weight in relation to body size rather than using mass alone. Squaring the height helps reduce the effect of taller people naturally having larger bodies, making the ratio easier to compare across different heights. It is a screening tool, not a direct measure of body fat, so it works best as a quick health indicator rather than a diagnosis.

Use BMI when you need a fast, standardised estimate of whether a person's mass is low, normal, or high for their height. It is commonly used in health checkups, fitness assessments, and basic epidemiology.

• Using height in centimetres instead of metres
• Forgetting to square the height before dividing
• Treating BMI as a direct measure of body fat or fitness