There are 72 bags of sand and 24 bags of cement in one cubic metre of concrete when created using a 3:1 mix ratio. This is calculated by taking the weight of a cubic metre of concrete and dividing it by the mix ratio that is being used.
For instance, concrete weighs approximately 2,400kg per cubic metre. If we divide this by four, which is the total number in our 3:1 ratio, it gives us the amount required for each part.
2,400kg/4 = 600kg therefore, we need 1,800kg of sand (3 x 600kg) and 600kg of cement (1 x 600kg). Divide these numbers by 25kg, the amount in each bag, to get the total number required to create 1m3 of concrete.
Bags Required for Different Blends of Concrete
Below is a table showing how many 25kg bags of sand and cement you require based on a range of different mix ratios.
|Mix Ratio||25kg bags of sand needed||25kg bags of cement needed|
Note: the numbers in the above table have been rounded up so that you do not underestimate the amount of materials required.
These mix ratios are suitable for a number of building applications, including render, screed, and bricklaying mortar. For a stronger grade of concrete incorporate ballast, which will create a much more durable final product.
Should Mixing Ratios Be Based on Volume or Weight?
It is important to note that the ratios refer to volume and not weight. However, cement and sand are close enough in density for weight to be used as a measurement.
Cement weighs 1440kg/m3 and sand weighs around 1600kg/m3. In this situation, using weight rather than volume makes mixing the concrete easier and saves time as you can measure your mixture using 25kg bags. These numbers will vary as on your sand-cement mix ratio, which changes depending on the end-use of the concrete.
If you do require enough sand to create one cubic metre of concrete, it would be cheaper to buy the sand in 800kg bulk bags rather than 25kg bags. This would save you up to 50% and approximately £125.