Features

Normal weight is usually determined by your body mass index (BMI). The BMI formula uses your weight and height to predict your percentage of body fat.

Formula

The formula for BMI is your Weight in Pounds, divided by the Square of your Height in Inches, multiplied by 703. Normal BMI, which is to say normal weight, produces a result that falls within the range of 18.5 to 24.9.

Limitation

Although BMI is considered a relatively accurate predictor of body fat percentage, its formula is based on averages and is not a direct measure of a person's percentage of body fat.

Misconceptions

Healthy weight is distinct from normal weight because it is possible to have a normal BMI along with an unhealthy percentage of body fat. It's also possible to be classified as overweight according to your BMI even though you have a perfectly healthy percentage of body fat. Healthy weight is determined not by your weight but by what your body fat percentage is relative to your gender.

Discrepancy

Since muscle weighs more than fat, people who actually have a healthy percentage of body fat but above average lean muscle mass might register as overweight according to BMI standards. On the flip side, people who have unhealthy percentages of body fat combined with poor muscle composition might register as being of normal weight even though they are actually at risk for obesity and overweight related health complications.

Tips

The skinfold test is one method of measuring your body fat percentage directly.

Source:

CDC: About BMI

UNM: Body Composition

Resource:

BMI Calculator

Skinfold Testing