This calculator doesn't measure your height and weight: you have to know how long you are and how heavy and then you can enter these measurements in the BMI calculator.
BMI is calculated by your weight divided by the square of your height.
THere are several other ways to measure yourself. Here on Sparkpeople you can also enter your hip, thighs, upperarm and waist measurements. Particularly the waist and hip are important measurements, because they can indicate whether you need to lose weight and if so, how much.
More info here: en.wikipedia.org/wiki/Waist%E2%80%93hip_ra