There’re many types of concrete and grades of concrete (e.g. Ready mix, Precast, Reinforced conc). In Calculation of concrete, first of all Multiply Length and Width & Hight to get Volume. It is same as Plaster/mortar calculation.
Let suppose a slab of single story house which has 50 feet length and 25 feet width.
Length= 50 ft
Width= 25 ft
Area of slab = L×W
Area of slab = 50’×25′ = 1250 sft or 138.9 sqyd
Thickness of slab = 6 inch = 0.5 ft (That commonly used)
Wet Volume of Concrete = Area × Thickness of slab
Wet Volume=1250×(6/12) = 625 Cft
- 6 divided by 12 to convert inch into foot
Dry Volume of concrete = 625×1.54= 962.5 Cft or 27.25 cu.m (35.31cft = 1 cu.m)
“It is compulsory to multiply with 1.54, to convert wet volume of concrete into dry volume (because addition & evaporation of water cause shrinkage in concrete mix, which ultimately decrease in volume).”
Dry volume means you need 962.5 Cft concrete for 25’x50′ slab.
How to calculate Yards of concrete?
- Calculate volume in Feet
- Multiply with 1.54 (to convert into dry volume)
- Divide by 27 to convert into Cubic Yards.
Now we will use dry volume in concrete calculation to get Quantity of Cement, Sand & Aggregate for 1:2:4 concrete mix calculation.
Ratio of concrete mix (Grade M15) = 1:2:4
Sum of ratio = 7
Cement quantity in Concrete:
- Quantity of Cement = (1÷7)×962.5 = 137.5 Cft
- Cement = (1÷7)×27.25 = 3.9 Cum
Density of cement = 1440kg/m3 or 40.77kg/cft
- Multiply cft with 40.77 & cum with 1440 to get quantity of cement in KGs.
Cft>>> 137.5×40.77= 5606 Kg
Cum>>> 3.9×1440= 5606 kg
How to calculate cement bags in concrete? To find cement Bags divide by 50 (50 kg in one bag of cement).
5606/50 = 112 bags of cement
Or directly calculate cement bags from Volume:
Volume of cement bag= 0.034cum or 1.226cft
Cft>>> 137.5÷1.226 = 112 Bags
Read also Plaster/mortar calculation.
Calculation of sand in Concrete:
- Quantity of Sand = (2÷7)×962.5 = 275 Cft
- Sand = (2÷7)×27.25 = 7.78 Cu.m
Density of sand is 1600kg/m3 OR 45.30 kg/cft
Read also Brick calculation.
Calculate aggregate quantity in Concrete:
- Quantity of Aggregate = (4÷7)×962.5 = 550Cft
- Aggregate = (4÷7)×27.25 = 15.57 Cu.m
Calculation of Water Cement Ratio in concrete:
- Water cement ratio means quantity of water against cement (in kgs).
- W-C Ratio = 50% × Quantity of cement (kg)
- Water= 5606×0.50 = 2803 liters.
50% of water quantity is commonly used in ordinary concrete mix , but it can be b/w 22% to 50%.