Computing number of CHB ( Concrete Hollow Blocks) of a Wall - Engineering Problem

Building a house is a detailed job. Every corner of the house or room needs a CHB or Concret Hollow Blocks. But is it enough to just produce numbers of hollow blocks without knowing the exact number the walls need?

How to solve the number of CHB in a wall?
First, we need to measure the wall we are planning to make. The next step is to compute the total area of the wall. If there are doors and windows, we just need to subtract the area of the doors and windows to the total are of the wall. The next step is to multiply the total area of the wall (already subtracted from the area of the doors and the windows) by the size of the Hollow Blocks.

After that, we will already know how many CHB (Concrete Hollow Blocks) will we need in order to build the wall.