Every new project starts with a big question: How much aggregate do you actually need? It might sound tricky, but with a few simple steps, you’ll have the answer in no time and avoid over-ordering or running short.
For ease of use, we’ve broken down the calculation into 5 easy-to-follow steps to save you money and help you calculate just how much recycled aggregate you may need.
Your 5-step guide for calculating how much aggregate you will need:
Step 1: Measure the area you will need covered
Start by calculating the total volume of the area or concrete you want covered with aggregate in cubic metres (or m³). Use the following formula:
Volume (cubic meters) = Length (m) × Width (m) × Depth (m)
For better understanding, here is a real-life scenario. For a slab measuring 10 meters in length, 10 meters in width, and 0.2 meters in depth:
- Volume = 10 m × 10 m × 0.2 m = 20 cubic meters
Step 2: Adjust the total according to dry volume
Remember that concrete components expand when they are mixed, so it’s standard practice to increase the calculated volume by a factor to account for this expansion. A common factor used in this calculation is 1.54:
Dry Volume = Wet Volume × 1.54
Let’s use our example in step 1 for clarity:
- Dry Volume = 20 m³ × 1.54 = 30.8 m³
Step 3: Calculate the concrete mix ratio
Concrete mix ratios may vary depending on the strength requirements. A typical mix ratio for any general construction is 1:2:4. In layman’s terms, this means:
- 1 part cement
- 2 parts sand (fine aggregate)
- 4 parts gravel (coarse aggregate)
The total parts in this mix are calculated as follows: 1 + 2 + 4 = 7 parts.
Step 4: Calculate individual material volumes
Using the previously calculated dry volume and the mix ratio, you can now calculate the volume of each component. Here’s how:
- Cement Volume = (1/7) × 30.8 m³ = 4.4 m³
- Sand Volume = (2/7) × 30.8 m³ = 8.8 m³
- Aggregate Volume = (4/7) × 30.8 m³ = 17.6 m³
Step 5: Convert Volumes to Weights
Now that you have the individual material volumes, it’s time to convert these volumes into weights. Remember that the density of cement is approximately 1440 kg/m³. Follow this formula to convert volumes to weights:
How to calculate how much cement you will need:
Cement weight = cement volume × approximate cement density
In this case:
- Cement weight = 4.4 m³ × 1440 kg/m³ = 6,336 kg
A standard bag of cement that you would find at your local store that is ready to mix would typically weigh 50 kg. With that in mind, here’s how to calculate how many bags of cement you would need to purchase to cover the total area:
- Number of bags = 6,336 kg / 50 kg/bag = 126.72 bags
In this case, you are better off rounding up to ensure that you have enough bags of cement to cover the entire area while accounting for any spillage. With this in mind, your total would be 127 bags of cement.
How to calculate how much sand you will need:
Assuming a sand density of 1600 kg/m³:
Sand weight = sand volume x sand density
In this case:
Sand weight = 8.8 m³ × 1600 kg/m³ = 14,080 kg
How to calculate how much aggregate you will need:
Finally, we get to the part where we can calculate aggregate. With an aggregate density of 1650 kg/m³, you can follow this formula:
Aggregate weight = aggregate volume × aggregate density
In this case:
Aggregate weight = 17.6 m³ × 1650 kg/m³ = 29,040 kg
Final tips for purchasing aggregate
We recommend ordering 5–10% extra to account for spillage, variations in mix, and unforeseen changes on-site.
For large-scale or complex projects, speak to the team at PP O’Connor. We’ll help you calculate exactly how much aggregate you need and guide you to the right solution, whether it’s 6F5 recycled aggregate or a bespoke mix, ensuring cost-effective, sustainable results.
