1 Meter 
10 Decimeter 
100 centimeter 
1 Decimeter 
10 centimeter 
100 millimeter 
1 Km 
10 Hectometer 
100 Decameter 
1 Decameter 
10 meter 
1000 centimeter 
1 square Meter 
100 square Decimeter 
10000 square centimeter 
1 square Decimeter 
100 square centimeter 
10000 square millimeter 
1 Hectare 
100 squareDecameter 
10000 square meter 
1 square myraimeter 
100 square kilometer 
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=(1/2)BH 
2 
Isosceles right angled triangle Equal side =a 
Height=a 
A=(1/2)a^{1/2} 
3 
Any triangle of sides a,b ,c 
P=a+b+c 
A=[s(sa)(sb)(sc)]^{1/2} s=(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=LX B 
6 
Parallelograms Two sides are given as a and b 
P=2a+2b 
A= BaseX height When the diagonal is also given ,say d Then A=[s(sa)(sb)(sd)]^{1/2} s=(a+b+d)/2 
7 
Rhombus Diagonal d_{1} and d_{2} are given 
p=2(d_{1}^{2}+d_{2}^{2})^{1/2} Each side=(1/2)(d_{1}^{2}+d_{2}^{2})^{1/2 } 
A=(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=[s(sa)(sb)(sc)(sd)]^{1/2} s=(a+b+c+d)/2 b)A=(1/2)d_{1}d_{2} where d_{1} and d_{2 } are the diagonal c)A=(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 isoceles traingle with equal side a  A=(1/2)a^{1/2} 
If it is equilateral triangel 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 