1. Mensuration Formulas for RECTANGLE

Area of Rectangle = Length × Breadth.                               


Perimeter of a Rectangle = 2 × (Length + Breadth)

Length of the Diagonal = √(Length2 + Breadth2)

2. Mensuration Formulas for SQUARE

Area of a Square = Length × Length = (Length)2 

Perimeter of a square = 4 × Length

Length of the Diagonal = √2 × Length

3. Mensuration Formulas for PARALLELOGRAM

Area of a Parallelogram = Length × Height

Perimeter of a Parallelogram = 2 × (Length + Breadth)

4. Mensuration Formulas for TRIANGLE

Area of a triangle=(1/2)(Base × Height)=(1/2)(BC×AD)

For a triangle with sides measuring a, b and c, respectively:
Perimeter = a + b + c

s = semi perimeter = perimeter/2 =  (a+b+c)/2

Area of Triangle, A=

(This is also known as “Heron’s formula”)
Area of isosceles triangle = 

(Where a = length of two equal side, b = length of base of isosceles triangle.)

Area of an equilateral triangle = 

(Where, a is the side of an equilateral triangle)
5. Mensuration Formulas for TRAPEZIUM

Area of a trapezium = (1/2) × (sum of parallel sides) × (distance between parallel sides)
= (1/2) × (AB+DC) × AE

Perimeter of a Trapezium = Sum of All Sides

6. Mensuration Formulas for RHOMBUS


Area of a rhombus=(1/2)×Product of diagonals


Perimeter of a rhombus = 4 × l
(where l = length of a side)

7. Mensuration Formulas for CIRCLE and SEMICIRCLE

In the following formulae, r = radius and d = diameter of the circle

Area of a circle = πr2= (πd2)/4

Circumference of a circle = 2πr = πd

Circumference of a semicircle = πr

Perimeter of the semicircle = (πr+d)

Area of semicircle =(πr2)/2 

Length of an arc = (2πrθ)/360, where θ is the central angle in degrees.

Area of a sector = (1/2) × (length of arc) × r = (πr2θ)/360






Part 1 deals largely with 2D formulas. You can also Read Part 2  of Mensuration Formula