1. The perimeter of a polygon (or any other closed curve, such as a circle) is the distance around the outside.
2. The area of a simple, closed, planar curve is the amount of space inside.
3. The volume of a solid 3D shape is the amount of space displaced by it.
Some formulas for common 2dimensional plane figures and 3dimensional solids are given below. The answers have one, two, or three dimensions; perimeter is measured in linear units, area is measured in square units, and volume is measured in cubic units.
Shape 
Formula 
Variables 
Square 
P = 4s 
s is the length of the side of the square. 
Rectangle 
P = 2L + 2W 
L and W are the lengths of the rectangle's sides (length and width). 
Triangle 
a + b + c 
a, b, and c are the side lengths. 
Right Triangle, with legs a and b (see Pythagorean Theorem) 
a and b are the lengths of the two legs of the triangle  
Circle 

r is the radius and d is the diameter. 
Shape 
Formula 
Variables 
Square 

s is the length of the side of the square. 
Rectangle 

L and W are the lengths of the rectangle's sides (length and width). 
Triangle 
b and h are the base and height .  
Triangle 
a, b, and c are the side lengths and s is the semiperimeter  
Parallelogram 

b is the length of the base and h is the height. 
Trapezoid 
b_{1} and b_{2} are the lengths of the parallel sides and h the distance (height) between the parallels.  
Circle 
A = πr^{2} 
r is the radius. 
Shape 
Formula 
Variables 
Cube 

s is the length of the side. 
Right Rectangular Prism 

L is the length, W is the width and H is the height. 
Prism or Cylinder 
V = Ah 
A is the area of the base, h is the height . 
Pyramid or Cone 
A is the area of the base, h is the height. 

Sphere 
r is the radius. 