When used to predict an individual's health, rather than as a statistical measurement for groups, the BMI has limitations that can make it less useful than some of the alternatives, especially when applied to individuals with abdominal obesity, short stature, or high muscle mass.īMIs under 20 and over 25 have been associated with higher all-cause mortality, with the risk increasing with distance from the 20–25 range. Major adult BMI classifications are underweight (under 18.5 kg/m 2), normal weight (18.5 to 24.9), overweight (25 to 29.9), and obese (30 or more). The BMI is a convenient rule of thumb used to broadly categorize a person as based on tissue mass ( muscle, fat, and bone) and height. The table may also show contour lines or colours for different BMI categories. The table displays BMI as a function of mass and height and may show other units of measurement (converted to metric units for the calculation).

The multiplication and division may be carried out directly, by hand or using a calculator, or indirectly using a lookup table (or chart).

The BMI may be determined first by measuring its components by means of a weighing scale and a stadiometer. The BMI is defined as the body mass divided by the square of the body height, and is expressed in units of kg/m 2, resulting from mass in kilograms (kg) and height in metres (m). Body mass index ( BMI) is a value derived from the mass ( weight) and height of a person.

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