A figure which is not uniform and regular in shape is where an irregular figure. There are several practical situations where it is necessary to estimate the area of the irregular figures. For example, the areas of plots of land, areas of indicator diagrams of steam engines and area of ships by naval architects, etc. Since, these areas can not be obtained by the simple application of a formula, so there are many methods where by the area of an irregular plane surfaces may be found and some of these include;

(a) Trapezoidal Rule                 (b) Simpson’s Rule