www.justforkidsonly.com 
HOME / SITE MAP / NEXT / BACK TO READY REFERENCE
 READY REFERENCE 
Surface Measurement
Perimeter and Area  2
Dear friend,
you must have noticed in the previous section that
by adding more lines or by bending the line
we can cover some area.
Thus we added one more dimension.
By adding one more dimension we made different shapes or two dimensional figures.
Two dimensional geometric figures now have Surface Area.
The surface area of any figure (two dimensional or three dimensional) is
the sum of all the areas of all the shapes that cover the surface of the object.
Surface area is measured in Square Units.
You have to keep in mind that while calculating the surface area you have to use the same units for all the measurements.
For example, you can not use inches for length and centimeters for the width.
There are different equations for different geometric figures to find out their surface area.
For example:
For square you multiply length x 4 = its surface area in square units.
For triangle you multiply length of its base x its height = its surface area in square units.
For Rectangle you multiply its length x its width = its surface area in square units.
For circle the equation is pi x r², where Pi is a constant. Pi = 3.141592... and r is radius of the circle.
Perimeter:
The distance around a figure is called its perimeter.
This is equal to the sum of its all sides.
Now let us see some of the equations for surface areas for some common geometric figures.
surface area = a x a = a², 
perimeter = a + a + a + a = 4 x a = 4a 

Square 

surface area = a x b = ab, 
perimeter = a + b + a + b = 2a + 2b = 2(a + b) 
Rectangle 


surface area = b x h = bh,  perimeter = a + b + a + b = 2a + 2b = 2(a + b)  
Parallelogram 
surface area = h/2 + (b1 + b2),  perimeter = a1 + b1 + a2 + b 2  
Trapezoid 
surface area = pi r x r = pi r², 
perimeter = pi x 2r = pi x d 

Circle  where d is diameter of the circle 
surface area = pi x r1 x r2
= pi r1r2, 
perimeter there is no simple exact formula  
Ellipse  Some formulas are simple but not exact, while some formulas are exact but not simple 
surface area = 1/2 x (b x h) = 1/2 (bh)  perimeter = a + b + c  
Triangle 
Surface area of a regular polygon = (1/2) x n x sin(360º/n) x s²,
where n = number of sides,
s = length from center to a corner
Table of Surface Measure
Traditional System
144 square inches = 1 sq. ft.
9 square feet = 1 sq. yard
30 1/4 sq. yds. = 1 sq. rod
160 sq. rods. = 1 acre
640 acres = 1 sq. mile
1 acre = 208.71 ft. x 208.71 ft.
Table of Surface Measure
Metric System
meter x 10 = decameter
meter x 100 = hectometer
meter x 1000 = kilometer
Conversion between metric and customary systems
CUSTOMARY  to  METRIC 
From  multiply by  To get 
square feet  0.0929  square meters 
square yards  0.8361  square meters 
square miles  2.59  square kilometers 
METRIC  to  CUSTOMARY 
From  multiply by  To get 
square kilometers  0.3861  square miles 
hectares  2.4710  acres 