Calculation of the materials required for construction is an important skill. This post focuses on how to calculate the amount of sand, cement and aggregate you will need for your construction.
Assume you need a concrete volume of 1 cubic metre, based on your dimension drawings. This is called the wet volume which is the volume of concrete after casting. To calculate the volumes required for the materials you will need to use the dry volume.
Assuming a mix design of 1:2:4, this means that the ratio of Cement to sand to coarse aggregate is 1:2:4. That is, 1 bucket of cement (Used as half a bag of cement in sites) is mixed up with 2 buckets of sand (20l) and 4 buckets (20l) of coarse aggregate. This mix design does not consider the cement grade used for the mix.
For 1 m3 of concrete, this translates to:
1.54 * 1 = 1.54 cubic metres of concrete.
To find the amount of material
Cement
Cement ratio /Total ratio= 1/7*1.54 =0.22m3
Taking the density of cement as : 1440 Kg/m3
Cement required = 1440 * 0.22m3
Total KGs required =316.8 Kg/m3
Cement bags(Assume 50KG bags) = 316.8/50 = 6.3 Bags of cement
Sand
Sand ratio/Total ratio =2/7 *1.54 = 0.44 m3
Taking the density of sand as 1680 Kg/m3
Sand required : 1680 * 0.44 =739.2 KG
Sand is sold in tonnes which is given by: Kgs required/1000 to give you the number of tonnes
Coarse aggregate/Ballast
Sand ratio/Total ratio =4/7 *1.54 =0.88 m3
Taking the density of sand as 1680 Kg/m3
Sand required : 1680 * 0.88 = 1478.4 KG
Ballast is sold in tonnes: Kgs required/1000 to give you the number of tonnes
Water
A good water ratio is 0.45/1 Water to cement volume.
Therefore Cement volume: 0.22m3
Water volume = 0.45 * 0.22 = 0.1 m3
Litres required are: 1000 * 0.1 = 100 Litres
Here are common design mixes used in Kenya for class 15 -40.
Read more on How to calculate the volume of sand and cement in mortar. If you are interested in concrete works, here is how you pour a slab on grade foundation.
Hoping this has been useful. Build Wisely!
