This document defines mensuration and provides formulas for calculating the perimeters and areas of various 2D and 3D shapes. It explains that mensuration deals with using formulas to calculate perimeters, areas, and volumes of plain and solid geometric figures. Formulas are provided for calculating the perimeters and areas of squares, rectangles, circles, triangles, parallelograms, trapezoids, cubes, cuboids, and cylinders. Some example problems are worked through applying these formulas to find perimeters and areas.