How to Work Out Body Mass Index

The Body Mass Index (BMI) is used to calculate a person's obesity level by comparing the height to the weight of a person. Many use this figure to pre-screen the health level of an individual, but it is not to mistaken with body fat percentage measurements. Using the general formula of weight / height² to come up with a number, you can measure yourself on the BMI scale. Scores under 18.4 are considered underweight according to the scale, the normal range is 18.5 to 24.9, overweight is 25 to 29.9, and obesity is 30 and over.

Things You'll Need

• Tape measure Scale Calculator

Instructions

1. Calculation for BMI is possible in the metric scale or the imperial. The first amount needed is your weight, measured in kilograms or pounds. If you measured your weight in pounds, multiply this number by 703. The weight in kilograms can be left as is. Refer to this number as Figure A. For example, with a weight of 150 pounds, multiply 150 by 703 for the amount of 105,450.

2. Measure height in terms of meters or inches. Square this number, or in other words, multiply this number by itself. Refer to this number as Figure B. For instance, a person who is 65 inches tall will multiply 65 by 65 for a total of 4,225.

3. Divide Figure A by Figure B for the score. In the example, 105,450 divided by 4,225 equals approximately 24.96.

4. Compare the total calculated to the BMI scale. In the example, this score is on the border of the normal and overweight ranges.

Tips & Warnings

• The scale value is based on adults over the age of 20. Healthy body mass index for children vary depending on age. A higher BMI score with age is typical but should not be over the upper end of the normal range.

• People with heavier muscle mass may find their BMI score on the upper end of the normal range or even in the overweight range despite a fit appearance and low body fat percentage.

References

• Centers for Disease Control and Prevention

Resources

• Body Mass Index Calculation for Adults and Children