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What's a Normal Body Mass Index for a Female?

Oct 23, 2009

If you are woman who is conscious about your weight and want to make sure your weight is at a healthy level, you should be informed about the body mass index for a female. While this is not a set number for everyone, there are ways to know your specific target and what it all means.

What Is a Body Mass Index?

The Body Mass Index (BMI) is a calculation, based on your height and weight as to the amount of fat on your body. Depending on the result, you can be classified as:

  • Underweight
  • Normal
  • Overweight
  • Obese

It is important to know where you stand on this scale, as having too much fat on the body can cause many health related issues. Now, the result you may find from a BMI Calculator online may seem odd at first, but this is a pretty good estimate.

Defining 'Normal'

BMI results are not based on a rigid set of numbers because everyone is different. The BMI is based on a a few key points:

  1. Sex of the person.
  2. Age of the person.
  3. Height of the person, in feet and inches. 
  4. Weight of the person.

All of these factors are taken into account when calculating a BMI score. In order to fit into the normal range for a woman, your results will fall into a percentage and that number is used to place you into one of the BMI categories mentioned above.

At the age of around 15 years, the BMI index for a normal result is around 16 to 17. As you age, the BMI changes as well:

  • 20 years: 24 – 26 BMI
  • 30 years: 26 – 27 BMI 
  • 40 years: 27 – 28 BMI 
  • 50 years: 28 – 29 BMI 
  • 60 years: 27 – 28 BMI

As can be seen, the normal ranking changes over time and, around the age of 57, it actually begins to drop again. This simply means there is no magic number, weight-wise that could cover a normal level for women as the BMI will change you age.

Defining the Numbers

Generally speaking, your BMI tells you your current weight status. Here are the rankings and what they mean:

  • Below 18.5 = Underweight
  • 18.5 - 24.9 = Normal
  • 25 - 29.9 = Overweight
  • 30 and above = Obese

Height has a direct effect on BMI because the taller you are, the more mass you will have. Since there is more mass, the ratio result of body fat will be different than someone who is shorter.

How To Calculate Your BMI

This is the forumla, in the imperial system for BMI calculation:

 

BMI =
( kg/m² )   
(weight in pounds * 703 )
————————————

height in inches²

This is the formula in the metric system:

 

BMI =
( kg/m² )
  weight in kilograms
  ————————————
  height in meters²

Is This Important?

We always hear about the dangers of being obese, but this type of information is also helpful to letting someone know when they are dangerously underweight. Being well underweight is a health hazard and using the BMI can let you know how much you would need to gain to return to a normal and healthy weight.

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