Determine the weight of an object. For example, a glass of water weights 200 g r a m s 200 \ \mathrm{grams} 200 grams net (not including the glass). Find out the volume of an object, e.g., by using the volume calculator. In our example, it's 200 c m 3 200 \ \mathrm{cm^3} 200 c m 3. Divide weight by volume. Summary. BMI is an estimate of body composition, based on weight and height. A moderate BMI for females is usually 18.5–24.9. People who know their weight and height can use a BMI calculator to What is the American average height of women? The average American female height is 163 to 164 cm, (approximately 64.2 to 64.6 inches), or around 5 foot – 5 inches tall. (for white females*). Why does the CDC webpage say the average height is 63.8 inches when you say that it is 64.5-ish. Em1dB6p.