BMI (Body Mass Index) is not a very good way to estimate body fat. It doesn’t account for bone mass or muscle mass. For example, a muscle-bound body may have a high BMI owing to the weight of the muscle, indicating obesity, even if body fat is low.
Enter the RFM (Relative Fat Mass). And all you need is a tape measure:
Men: 64 – (20 x (height/waist)) = RFM
Women: 76 – (20 x (height/waist)) = RFM
Height and waist measurements are in meters.
“An RFM ≥33.9 for women and ≥22.8 for men showed a high sensitivity to identify individuals with obesity.”
Remember to always calculate what’s inside the parentheses first. Then, from my engineering days: MDAS (multiply, divide, add, subtract) <– in that order.
A person who is 5’4″ and has a 28″ waist has an RFM of 30.3. (You can convert inches to meters easily on Google.)
76 – (20 x (1.6256/0.7112) = 30.3
Since 30.3 is less than 33.9, it does not indicate obesity.
WikiHow has a good how-to for measuring your waist.
Use your fingers to find the top of your hips and the base of your rib cage. Your waist is the soft, fleshy section between these two bony parts. It will also be the narrowest part of your torso and it is often located at or above your belly button. Exhale and then check the measurement on the tape.