A quick method to realize if you are fat and how much, is to determine your body mass index, or BMI as is known. It's described by the formula
Weight / Height2
where weight is expressed in kilograms and height in meters. All you need is just a simple calculator. You can also use right now the On Line BMI Calculator.
Regardless of the calculation above, in the following charts you can see approximately your ideal weight range according to your sex, height and frame. There is also a general rule that may be for you more convenient than these charts: keep your waist circumference to less than half your height.