One metre can be divided into 10 decimetres (dm), 100 centimetres (cm) or 1000 millimetres (mm) 100 m equals to 1 hectometre (hm) while 1000 m is 1 kilometre (km). The basic unit of length in the metric system is the metre (m). A diameter (d) is a straight line which divides the circle in two equal parts.Ĭalculate the surface area of a circle with a diameter of 3 m. Whereby d is the diameter of the circle and p (a Greek letter, pronounced Pi) a constant ( p = 3.14). The surface area or surface (A) of a circle is calculated by the formula:Ī (circle) = 1/4 ( p x d x d) = 1/4 ( p x d 2) = 1/4 (3.14 x d 2). Note that A = A 1 + A 2 + A 3 = 1 + 6 + 2 = 9 cm 2 Splitting a trapezium into one rectangle and two triangles. Number 4 is the same as number 1 but upside down.Īnother method to calculate the surface area of a trapezium is to divide the trapezium into a rectangle and two triangles, to measure their sides and to determine separately the surface areas of the rectangle and the two triangles (see Fig.

Note that the surface areas of the trapeziums 1 and 4 are equal. 1.Ĭalculate the surface areas trapeziums nos. In a trapezium only the base and the top run parallel.Ĭalculate the surface area of trapezium no. The top (a) is the side opposite and parallel to the base (b). The surface area or surface (A) of a trapezium is calculated by the formula:Ī (trapezium) = 0.5 (base + top) x height = 0.5 (b + a) x h. 5).Ĭalculate the surface areas of the rhombus and the parallelogram (see Fig. In a parallelogram the lengths of the opposite sides are equal none of the angles are right angles opposite sides run parallel (see Fig. In a rhombus the lengths of all four sides are equal none of the angles are right angles opposite sides run parallel. The surface area or surface (A) of a rhombus or a parallelogram is calculated by the formula:Ī (rhombus or parallelogram) = base x height = b x h. 4) has a surface area of 100 m x 100 m = 10 000 m 2 = 1 ha. For example, a field with a length of 100 m and a width of 100 m 2 (see Fig. By definition, 1 hectare equals 10 000 m 2. Related to irrigation, you will often come across the expression hectare (ha), which is a surface area unit. 3).Ĭalculate the surface areas of the rectangle and of the square (see Fig. Note that in a square the length and width are equal and that in a rectangle the length and width are not equal (see Fig. In a rectangle, the lengths of the opposite sides are equal and all four angles are right angles. In a square the lengths of all four sides are equal and all four angles are right angles. The surface area or surface (A) of a square or a rectangle is calculated by the formula:Ī (square or rectangle) = length x width = l x w. Surface areas can also be expressed in square decimetres (dm 2), square metres (m 2), etc.Ĭalculate the surface areas of the triangles nos. The surface of these triangles is expressed in square centimetres (written as cm 2).

2 have the same surface the shapes of the triangles are different, but the base and the height are in all three cases the same, so the surface is the same. 2) but the same formula is used for all of them.Ĭalculate the surface area of the triangles no. The surface area or surface (A) of a triangle is calculated by the formula:Ī (triangle) = 0.5 x base x height = 0.5 x b x h. The height (h), base (b), width (w), length (1) and diametre (d) of the most common surface areas In the case of a circle the expression diametre (d) is used (see Fig. In the case of a square or a rectangle, the expression length (1) is commonly used instead of base and width (w) instead of height. An example of a right angle is the corner of this page. The height is always perpendicular to the base in other words, the height makes a 'right angle' with the base. The height (h) of a triangle, a rhombus, a parallelogram or a trapezium, is the distance from a top corner to the opposite side called base (b). This Section will discuss the calculation of some of the most common surface areas: the triangle, the square, the rectangle, the rhombus, the parallelogram, the trapezium and the circle (see Fig. It might be necessary to calculate, for example, the surface area of the cross-section of a canal or the surface area of a farm. It is important to be able to measure and calculate surface areas. Surface areas of canal cross-sections and farms

Area of rectangle formula