Mensuration Class 6 Notes CBSE Maths Chapter 10 [Free PDF Download]

• Perimeter is the total length of the boundary forming around a closed figure, going round the figure once.

1. Perimeter of a rectangle\[\text{= 2  }\!\!\times\!\!\text{  }\left( \text{length + breadth} \right)\text{ }\!\!~\!\!\text{ }\]

2. Perimeter of a square \[\text{= 4  }\!\!\times\!\!\text{  length of its side}\]

3. Perimeter of an equilateral triangle \[\text{= 3  }\!\!\times\!\!\text{  length of a side }\!\!~\!\!\text{  }\!\!~\!\!\text{  }\!\!~\!\!\text{  }\!\!~\!\!\text{  }\!\!~\!\!\text{ }\]

4. Perimeter of a regular pentagon  \[\text{= 5  }\!\!\times\!\!\text{  length of a sides}\]

• Regular closed figures are those with the same number of sides and angles on all sides. 

• The area of a closed figure refers to the amount of surface it covers. 

• The following conventions are used to compute the area of a figure on squared paper:

1. Parts of the area that are less than half a square should be ignored.

2. If a region contains more than half a square. It should be counted as one square. 

3. Take the size of the square in sq units if exactly half of it is counted.

Here to make this closed figure, we can see, there are 16 squares are unused (uncut squares outside the figure), 4 squares are half used (squares cut in halves) and 4 squares are fully used (uncut squares inside the figure).

Area $=4+\dfrac{1}{2}\times 4=6$ units

• Area of a rectangle\[\text{= length  }\!\!\times\!\!\text{ breadth }\!\!~\!\!\text{ }\]

• Area of a square \[\text{= side  }\!\!\times\!\!\text{  side }\!\!~\!\!\text{ }\]