If you've ever been to fitness centers or you're a health-conscious person, then you've probably encountered this before.
Body Mass Index or BMI is a measure for getting a quick idea of whether your weight is just right for your height. Contrary to what others might have popularized it for, its not for calculating the percentage of body fat. It was presumed that if you have a greater BMI than normal, then you have higher fat content.
Wikipedia defines it as such:
The body mass index (BMI), or Quetelet index, is a heuristic proxy for human body fat based on an individual's weight and height. BMI does not actually measure the percentage of body fat. It was devised between 1830 and 1850 by the BelgianpolymathAdolphe Quetelet during the course of developing "social physics". Body mass index is defined as the individual's body mass divided by the square of his or her height. The formulae universally used in medicine produce a unit of measure of kg/m2. BMI can also be determined using a BMI chart, which displays BMI as a function of weight (horizontal axis) and height (vertical axis) using contour lines for different values of BMI or colors for different BMI categories. -- http://en.wikipedia.org/wiki/Body_mass_index
There is actually two ways of determining your health in terms of figures. Some watch their weight by frequently weighing in using scales. The other way to measure your health in terms of numbers (which is what I usually prefer) is by measuring sizes. Its just a matter of preference to either use the scale or use a tape measure.
My personal opinion is that, you might become heavier if you focus more on taking in proteins for muscle build up; hence the scale might not be an efficient measure. On the other hand, keeping measurements by the tape around particular sections of the body can help you to easily identify those that require trimming.
At any rate, you can always start out by determining your next steps to become more health conscious by gauging whether you have a normal BMI. I found this interesting chart from a flyer of Fern products.
And if your figures aren't found in this chart, there's another way to get your BMI. You can try this formula: