A body mass index, known as BMI in short, is an evidence-based method of calculating a person's body fat based on height and weight. Measuring a person's BMI has become more and more important as one of the shifting focuses of health is keeping people's body fat and weight under control. A person's BMI is calculated by converting a person's weight into kilograms, and dividing the weight by the square of a person's height in meters. The end result is then used to determine how much body fat a person approximately has; in essence, it helps measure how overweight a person is. This formula was derived through empiric studies made on many people in years past. For adults, a BMI of 18.5 to 25 is considered normal. A BMI of 25 to 30 is considered overweight, and a BMI of 30 or above is considered obese. Children's BMI are compared to other typical BMI values for their age. When trying to calculate BMI values for many people, a BMI calculator can come in very handy. In the US, weight is measured by pounds (lbs) and height is measured by feet and inches. Though the conversion to metric units is fairly straightforward, having to calculate these measurements over and over again can become tedious. Even after the conversions, the BMI still has to be calculated. Using a BMI calculator to take care of the conversions and math makes figuring out BMI values quick and easy. Note that using a BMI calculator should only be a way to help put together a picture of a patient's overall body size. It alone should not be used to determine if someone is obese. Despite their usefulness in clinical and weight loss measurements, BMI values do have their limitations. For instance, BMI tends to portray body fat higher than actual values for athletes and bodybuilders (due to their increased lean muscle weight), and may give skewed values for people of abnormal height. Still, using a BMI calculator is a handy way of quickly calculating and tracking a person's body fat goals.