1. A method of measuring a mean-to-target (MTT) based on pattern area measurements, the method comprising: providing a design pattern; measuring a plurality of the design pattern measurements for calculating an area of the design pattern based on a shape of the design pattern; calculating a series of calculation measurements by continuously substituting a same variation into the plurality of the design pattern measurements, and calculating a series of calculation areas corresponding respectively to each of the series of calculation measurements to generate a database including the calculation measurements and the calculation areas; forming an actual pattern using the design pattern; measuring an area of the actual pattern; selecting a calculation area from the series calculation areas, corresponding to the area of the actual pattern, from the database and selecting calculation measurements from the series calculation measurements corresponding to the selected calculation area; and calculating a difference between the plurality of the design pattern measurements and the selected calculation measurements and setting the difference as an MTT, wherein the providing, measuring, calculating, forming, measuring, selecting and calculating are performed on at least one processor.