1. Quadrilaterals - Square
All four sides of a square are equal.
All four angles of a square are right angles.
Perimeter of a square = 4 × s units (s = side)
Area of a square = s2 sq. units (s = side)
Diagonal of a square = sqrt(2) × s (s = side)
Diagonals of a square are equal and bisect each other in right angle.

2. Quadrilaterals - Rectangle
Opposite sides of a rectangle are equal.
All four angles of a rectangle are right angles.
Perimeter of a rectangle = 2 × (l + b) (l = Length, b = Breadth)
Area of a rectangle = l × b (l = Length, b = Breadth)
Diagonal of a rectangle = sqrt(l2 + b2) (l = Length, b = Breadth)
Diagonals of a rectangle are equal and bisect each other (not in right angle however).
Square is a special type of rectangle with l=b. D A b B l C

3. Quadrilaterals - Rhombus
All sides of a rhombus are equal. (All angles are not right angles however)
Opposite sides of a rhombus are parallel to each other.
Perimeter of a rhombus = 4 × s (wh. s = side)
Area = s × h (Wh. s=side, h=height)
Area = ½ × (d1 × d2) (wh. d1 and d2 are diagonals)
Diagonals of a rhombus bisect each other in right angle. (However they are not equal)
Opposite angles of a rhombus are congruent. Angles on either side are supplementary. A D d1 h d2 B C s

4. Quadrilaterals - Parallelogram
Opposite sides of a parallelogram are equal. (All angles are not right angles however)
Opposite sides of a parallelogram are parallel to each other.
Perimeter of a parallelogram = 2×(s1 + s2) (wh. s1 & s2 are sides)
Area = s1 × h (wh. s1 = side and h = corresponding altitude)
Opposites angles of a parallelogram are congruent, consecutive angles are supplementary.
Diagonals bisect each other. A D d1 h s2 d2 B C s1

5. Quadrilaterals - Trapezium
A quadrilateral which has at least one pair of parallel sides.
Parallel sides of trapezium are called bases and non-parallel sides are called legs.
Altitude of trapezium is the perpendicular distance between two bases.
Area = Average width × altitude (or height) = [(s1 + s2)/2] × h A s2 D h B C s1

6. Quadrilaterals - Kite A
A quadrilateral with two distinct pairs of equal adjacent sides.
Angles between unequal sides are equal.
In the figure above notice that ∠ABC = ∠ADC no matter how how you reshape the kite.
Area = (d1 × d2) / 2 B D d1 d2 C