1 Meter 
10 Decimetre 
100 centimetre 
1 Decimetre 
10 centimetre 
100 millimetre 
1 Km 
10 Hectometre 
100 Decameter 
1 Decameter 
10 meter 
1000 centimetre 
1 square Meter 
100 square Decimetre 
10000 square centimetre 
1 square Decimetre 
100 square centimetre 
10000 square millimetre 
1 Hectare 
100 squareDecameter 
10000 square meter 
1 square myraimeter 
100 square kilometre 
10^{8} square meter 
N 
Shape 
Perimeter/height 
Area 
1 
Right angle triangle Base =b, Height =h Hypotenuse=d 
$P=b+h+d$ Height =h 
$A=\frac {1}{2}BH$ 
2 
Isosceles right angled triangle Equal side =a 
Height=a 
$A=\frac {1}{2} \sqrt {a}$ 
3 
Any triangle of sides a,b ,c 
$P=a+b+c$ 
$A=\sqrt {s(sa)(sb)(sc)}$ $s=\frac {a+b+c}{2}$ This is called Heron's formula (sometimes called Hero's formula) is named after Hero of Alexandria 
4 
Square Side =a 

$A=a^2$ 
5 
Rectangle of Length and breath L and B respectively 
$P=2L +2B$ 
$A=L \times B$ 
6 
Parallelograms Two sides are given as a and b 
$P=2a+2b$ 
$A= Base \times height$ When the diagonal is also given ,say d Then $A= \sqrt {s(sa)(sb)(sd)}$ $s=\frac {a+b+d}{2}$ 
7 
Rhombus Diagonal d_{1} and d_{2} are given 
$p=2 \sqrt {d_1^2+d_2^2}$ Each side=$ \frac {1}{2} \sqrt {d_1^2+d_2^2} $ 
$A=\frac {1}{2} d_1 d_2$ 
8 
Quadrilateral a. All the sides are given a,b,c ,d b. Both the diagonal are perpendicular to each other c. When a diagonal and perpendicular to diagonal are given 
a. $P=a+b+c+d$ 
a. $A=\sqrt {s(sa)(sb)(sc)(sd)}$ $s=\frac {(a+b+c+d)}{2}$ b. $A=\frac {1}{2} d_1 d_2$ where d_{1} and d_{2 } are the diagonal c. $A=\frac {1}{2} d(h_1+h_2)$ where d is diagonal and h_{1} and h_{2} are perpendicular to that 
If you know the altitude and Base 
Area =(1/2)BH 
If you all the three sides 
A=[s(sa)(sb)(sc)]^{1/2} s=(a+b+c)/2 
If it is isosceles triangle with equal side a  A=(1/2)a^{1/2} 
If it is equilateral triangle with equal side a  A=[(3)^{1/2 }a^{2}]/4 
If it is right angle triangle with Base B and Height H  Area =(1/2)BH 