In skin fold analysis special calipers pinch different parts of the body. Skinfold calipers measure the thickness of your subcutaneous fat the fat underneath the skin at certain body locations.

Overweight Wikipedia
Direct measurement of total body fat. There are a number of proposed formulae that relate body fat to bmi. Skin fold analysis. Body fat via total body water this is a direct method for body fat measurement and it is easy to perform as it doesnt require any real participation on your side. Body fat can be estimated from body mass index bmi a persons mass in kilograms divided by the square of the height in meters. Measurements are taken at either 3 or 7 different sites on the body. If weight is measured in pounds and height in inches the result can be converted to bmi by multiplying by 703.
The body fat percentage bfp is the total mass of fat divided by total body mass times 100. For example if your waist is 30 your hips are. This method is made possible because a relationship exists between subcutaneous fat and the total amount of body fat3 thus you can estimate total body fat by measuring the fat under the skin. Essential body fat and storage body fat. To calculate body fat percentage add your waist and hip measurements and then subtract the neck measurement to determine your circumference value. Total body fat includes two types of fat.