If you want a quick way to check if you're under or overweight then install Body Mass Index on your phone.
This free app calculates your body mass index (BMI) instantly. All you need to do is enter your height and weight and click 'Calculate' from the Options menu. Besides giving you the BMI figure, the program will display in words whether you're underweight, overweight or just the right weight.
The scope of Body Mass Index is very limited. In fact, it does nothing more than calculate your BMI. It does keep records of your calculations though for future reference, and you can switch between metric and imperial units of measurement.
If you want a quick way of checking how fat you are though, Body Mass Index lets you do so very quickly.