On a construction site it may become necessary to estimate the number of blocks required for the construction of a wall. To do it correctly you will need to read the construction plan or building plan and section drawing. From the building plan you will need to know;
- The length of the wall
- The height of the wall
- The thickness of the wall
- Window or door spaces within the wall unit.
In most cases, the thickness of the wall is not required unless the wall thickness is greater than the width or thickness of the block.
How to estimate the number of blocks using AREA METHOD
This method requires that you know the number of blocks required to construct 1m2 of wall. For a normal block size of length 450mm, height 225mm, and width 225mm, with thickness of wall the same as the block, there is approximately 8 blocks per 1m2. Simply put; 8 blocks per m2
The above result was obtained practically, however other calculations report a value of between 8-10 blocks per m2 .
How to practically obtain the number of blocks per unit area
You can obtain the result practically, look for an already constructed wall of similar type you want to build. The wall should still show the exposed block work, or is not yet rendered. Then with a builders square or builder’s level, draw a square of 1m dimension on the wall using a chalk or erasable material. The square you draw should have an area of 1m2 .Next, count the number of blocks that fall within the square. The result you get is the number of blocks per square meter. This method works for any size of block or brick.
Now that you have the amount of blocks per m2 , look at the building and section plan then calculate the area of the wall using the area formula of length x height . From this wall area, deduct any area of door and window spaces. Finally multiply the wall area by number of blocks per unit area or per m2 . (note the unit)
Formula for number of blocks required = (Area of wall) X (no. of blocks per unit area)
A wall of length 5m and height 3m will have an area of
5m X 3m = 15m2
Therefore number of blocks = 15m2 X 8 = 120 Blocks.
How to estimate the number of blocks using DIMENSION METHOD
This method involve using the block dimensions to estimate the number of blocks required for a wall construction.
Lets assume you are required to estimate the number of blocks in foundation required to fence a plot of land. Block will be laid in stretcher bond. The height of wall in foundation being about 450mm. and we are to use block size of length 450mm, height 225mm, and width 225mm. The dimensions of the plot of land being 30m by 15m. Here is what you do;
Perimeter of plot of land;
2 X (30+15)m = 90m
Since the wall will be constructed in stretcher bond, you will just divide the perimeter of the plot of land by the length of the block;
90m / 0.45m = 200 blocks ( note; 450mm is converted to m by dividing it by 1000)
This 200 blocks is the approximate number of blocks required for the 1st layer in foundation.
Since the height of wall in foundation is 450mm, it means we will have 2 layers of blocks in foundation i.e. 450mm / 225mm (height of block) = 2
Hence total blocks required for foundation is 200 blocks X 2 = 400 blocks