Surface area of Cuboids


Finding the surface area of cuboids can appear on either the calculator or non calculator paper of your maths exam.  A common mistake is to confuse this topic with finding the volume of cuboids; these are two totally different questions!



Example Question

A cereal box has length 20 cm, height 30 cm and width of 8 cm.
Find the surface area of the box.



Solution
To find the surface are of the box we need to find the area of each rectangular face and add them all up.

The area of the front face is 20 x 30 = 600 cm2.
The area of the top face is 20 x 8 = 160 cm2.
The area of the side face is 8 x 30 = 240 cm2.

Now add these together to get 600 + 160 + 240 = 1000 cm2.

IMPORTANT: This is not our final answer! Cuboids have 6 faces in total.  We have only added three so far!  For every front there is a back, for every top there is a bottom, and for every side there is another other side.

This means we need to double our answer to get 1000 x 2 = 2000 cm2.


Test Yourself!






A shoe box has length 30 cm, height 15 cm and width of 18 cm.
Find the surface area of the box.




cm2


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