ya mam
no, you can use waist circumference
For just a rough estimation, stick with the tried and true skin fold measuring. If you want a more accurate reading and are willing to put up with the hassle, see if a local university offers hydrodensitometry testing.
Short answer: they don't. They're just very convienent. If you want an accurate measurement you can do at home, use the skin flap measuring technique. If you're willing to put up with the hassle, look into hydrodensitometry testing or DXA (dual-energy x-ray absorptiometry)
One of the most common ways for one's body fat to be represented is with BMI. This number is calculated based on an individual's height and weight and is used as a quick way to estimate whether or not he or she is at a proper weight. Although it is useful as a quick tool, the reality is that it can be quite inaccurate. The reason is that it does not actually represent how much body fat one has on his or her body, but rather bases it on an approximation of how much body fat the person probably has at his or her height and weight. Based on the above reasoning, BMI can offer a useful representation of whether or not one is within a healthy weight range, but in order to get an actual representation of body fat a different method is probably necessary. Fortunately, there are many other tools that can be used to measure body fat that range from very inexpensive options that can be used in one's home, to very expensive options that might require a doctor visit. If a more inexpensive test is desired, a great option is a set of calipers. With this tool one can take measurements of body fat around his or her body and use an equation to give a more accurate idea of body fat percentage. In addition to calipers, inexpensive scales are currently being sold which can measure body fat percentage. These are known to be somewhat inaccurate, but in some cases can offer a more accurate measure of body fat than BMI. If one desires the most accurate body fat measure possible, there are various tests that can be performed by a doctor or specialist. One such method is called hydrodensitometry weighing and involves being weighed both in and out of water. Due to the fact that bone, fat, and muscle have different densities, an accurate idea of the body fat one has one his or her body can be obtained. As would be expected, this test is very accurate but can also be very expensive. For the above reasons, it is best for anyone using BMI to understand exactly how it was calculated. A high or low number does not necessarily mean one is at a healthy weight and other tools should probably be utilized. With a proper idea of one's healthy weight range, the necessary dietary and lifestyle adjustments can be made to either reach or maintain that healthy body weight.