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How to Calculate/Quantify The Total Number of Bags of Portland Cement, Quantity of Fine Aggregate (SAND) in Kilograms/Tons and Coarse Aggregate (GRANITE) That are in a Concrete Slab.

Do you wish to know the amount of cement, Sand and concrete needed for your current project?

You can know what is needed even before going into it.

We will show you how to calculate each of these one after the other.

Tons of granites and sand


Concrete mix ratio simply means the amount by volume of cement, fine aggregate (which can be sharp sand) and coarse aggregate (which can be granite, gravel, etc). 

For example:

A concrete mix ratio of 1:2:4 simply means to every 1 head-pan of cement you need to mix 2 head-pans of sand and 4 head-pans of granite. 

Similarly a concrete mix ratio of 1:1.5:3 means for 1 head-pan of cement you need to mix 1.5 head-pans of sand and 3 head-pans of granite.

Estimating the Quantities of Portland Cement, Sand and Gravel from Building Plan, first calculate the volume of Concrete to know the quantity of cement, sand and granite that you need for the work.

Using concrete strength of M10 which is Mix ratio 1:3:6 to calculate the concrete mix of a slab

In figures 1 and 2 

If a Slab thickness is 300mm = 0.30m, 

the width is 4000mm = 4m and 

the Length is 5000mm =5m.

Volume of Concrete 

= length x width x thickness 

= 5m x 4m x 0.30m = 6m³.

Calculating the Volume of Portland Cement in the Concrete:

To get the volume of cement in the concrete using mix ratio 1:3:6,

Sum up the numbers in the mix-ratio which is 

1+ 3 + 6 = 10.

To get the volume of the Portland cement used in the concrete we have to divide the volume of the concrete by the total parts in the mix-ratio:

Volume of cement in the concrete 

= 6m³ x ¹/10 

= (6/10)m³

= 0.6m³.

Density of one bag of cement = 1440kg/m³

Mass of one bag of cement = 50Kg.

Density = mass/volume

(ρ = m ÷V)

V = m ÷ ρ

V = 50kg ÷ 1440kg/m³

= 0.0347m³ = 0.035m³ approximately.

To get the numbers of bags of cement that was used we simply divide the volume of cement in concrete by the volume of one bag of cement which is

(0.6m³)/ (0.035m³) 

= 17.29 bags

 = (17 + 2)bags 

= 19 bags of cement.

Adding 2 bags of cement which is 10% of 17 bags of cement as wastage, we get the total number of  bags of cement needed for the concrete to be 17 bags + 2 bags 

= 19 bags of cement.

To calculate the Quantity of fine aggregate (Sand):

Recall that from our concrete mix ratio of 1 part cement, you need 3 parts of sand. That is, for every 0.6m³ of cement, you need:

0.6m³ x 3 = 1.8m³ of sand.

The Dry Loose Bulk Density (DLBD) of sand 

DLBD = 1762kg/m³.

The quantity of sand that is in the concrete

 Mass = Volume x Density

Mass = 1.8m³ x 1762kg/m³ 

= 3171.6kg of sand.


1kg of sand = 0.001ton


3171.6kg =  3.17 tons 

We need about 4 tons of fine aggregate(Sand) for the work to be done completely.

Calculating the quantity of coarse Aggregate (Gravel or Granite): 

Also recall that from our mix ratio for every 1 part cement, we need 6 parts of granite. That is,

for 0.6m³ of cement, we need:

0.6m³ x 6 = 3.6m³ of Granite.

Bulk Density of Granite is still the same as the Bulk Density of Sand which is equal to 1762Kg/m³.

The quantity of Granite we need = 1762Kg/m³ x 3.6m³ 

= 6343.2kg

= 6.34 Tons = about 7 Tons of Coarse Aggregate (It could be Granite or Gravel) will be needed to cast the concrete slab.

Therefore 19 bags of cement, 4 Tons of fine aggregate and 7 Tons of coarse aggregate are needed to cast the concrete of 5m Length, 4m width and 0.30m thickness.

You can still apply this method in calculating the number of bags of Portland cement, granite and sand needed for Pillars and beams as well.

Also read: How to calculate the amount of cement and sand for plaster wall

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