How to calculate numbers of blocks from a building plan.

Most asked question from a would be house owner is always how many blocks do I need to get my building completed. Hence this topic is written with illustrations to make it easy for you to dothe calculations yourself from the plan your architect gave you.

The plan above is for a 2 bedroom bungallow, so we are going to start from the basics having inmind these factors-

i)The lenght of a block is 0.45m or 450mm or 18″ii)The width of thickness varies -150mm or 6″ and 225mm or 9″ which are most common.ii)Taking for a general or average purpose, the blocks laid from foundation to dpc(german oroversite concrete) is 4 coaches/levels. From dpc to the base of window another 4 coaches,frombase of window to top of window another 5 coaches, then from top of window to base of roofanother 3 coaches, neglecting the lintel or concrete on top of window.Now with these parameters let calculate the plan above which has a wall of 150mm or 6″ allthrough.

Add the length and breadth of the blockwall for external and internalTherefore (A)9,400mm +9,600mm(B)+9400(C)+9600(D)=38,000mm or 38mNow add the internal walls too(Follow the grid lines and check the corresponding dimensions on plan remember 150mm is theblock width)

(Grid 7)150+3600+150+150+3600+150=7,800mm or 7.8m

(Grid 6)1350+150+2250+150+825+675+150=5,550mm or 5.55m

(Grid 1b)800+2400+1300+900+100=5,500mm or 5.5m

(Grid 2)2600+900+100+150+100+900+500+150=5,400mm or 5.4m

(Grid 3)1800+150+650+900+250+900+1450=6,100mm or 6.1m

(Grid 3b-Kitchen)900+50+1200+50+150=2,350 or 2.35m

(Grid 7b toilet)1800 or 1.8m

Total internal walls=34,500mm or 34.5m

Therefore Total walls=38,000mm +34,500mm=72,500mm or 72.5m

Now for the first 4 coaches to dpc level the wall will run right through, i.e the spaces fordoors or windows are not left out (n/b- blocks are used in relatively strong and stable soil notwaterlogged area that requires concrete instead).

Divide the sum by 450mm to know the numbers needed for one level/layer/coach of blocks72,500/450=161 blocks

From dpc level to roof lets take the numbers of coaches to be 4+5+3=12 coachesthen multiply the numbers of blocks for each coach above by 12161 x 12=1932 blocksDon’t forget we have windows and doors spaces which we need to remove,for each window of 1200mmtake numbers of the block to be 14 (i.e 1200/230=5.2 and 1200/450=2.6 ,5.3 x2.6=14 approxNow count the numbers of 1200mm windows and multiply by 14Total numbers of 1200mm windows as counted on plan is 12 (note 2400mm window was taken as two of1200mm window)

i.e 11 x 14 =154 blocks + 7 blocks for 600mm window for toilet. Total=161 blocksNow calculate for doors,Numbers of blocks for a door of 900mm is 18.height of a door(2100/225=9)+width of a door (900mm/450mm=2). so 9 x2 =18 blocks for each door.

ultiply 18 by numbers of doors=18 x8=144 blocks

Add 144+161=305 blocks,then remove from total blocks of 644 (for dpc) + 1932

Total numbers of blocks reqd=2,271 blocks

For a quick calculation, having the entire length to be 72,500mm. Take for a bungallow total

lenght from foundation to roof to be 1,200mm +3000mm=4200mm

Then calculate the surface area which is 72,500 x 4200 and convert to meters72.5m x 4.2m=304.5m2

Remove surface areas of windows and doorsFor window, height is 1.2m and total is 11

i.e 1.2m x 1.2m x 11=15.84m2 +0.6 x0.6(toilet window)=16.2m2

For doors, height is 2.1m while width is 0.9m

i.e 0.9 x 2.1 x 8(nos of doors)=15.12

Total area for doors and windows=16.2m2 +15.12m2=31.32m2

Remove 31.32m2 from 304.5m2=273.18m2

Now divide this by surface area of a block which is 0.225 x 0.45=0.10125

The blocks reqd caculated by this method is 273.18m2/0.10125=2,698 blocks

Note a difference of about 400 blocks from the two calculations. Of course you can’t get exactlythe numbers you need but the first method is close to it. And calculations are not 100% truebecause of these factors

1-The mortar space was not considered2-Blocks that will be wasted due to breakages e.t.c