Making a concrete budget yourself keeps you updated on how much money the planned structure is going to cost.
While we can't avoid spending money on construction materials, we can certainly reduce unnecessary purchasing costs by a perfect estimation.
The article contains a footing calculation method, estimating tricks of the total weight of concrete bags you need to cover a certain amount of surface, and basic calculation methods so that you can estimate the volume by yourself.
Basics of Concrete Calculation
Calculating how much concrete do you need for a project is easier than you think. The calculation is simple math of three variables, height, width, and the length of the concrete block you intend to make.
Multiplying the height, width and length of the concrete slab will give you the total volume of concrete you need for the project.
How Many Bags of Concrete Are in A Yard?
A bag of 80 lbs concrete can cover 0.5 to 0.6 cubic feet of the surface. As you know that a cubic yard equals 27 cubic feet, you will need forty five 80Lbs bags of concrete to cover a yard surface.
On the other hand, if you intend to go with smaller concrete bags, then it will take 60 bags of 60Lbs concrete to fill up a yard of surface.
However, we always recommend buying an additional 5 to 10% of construction materials than estimated. Otherwise, you may end up having difficulty finishing the project because of losses in transportation, mixing, and application.
Things to Remember before Calculating Concrete
How Thick Concrete Slab Do I Need For Durability?
You will see 2 different thicknesses of concrete slabs generally, i.e. 4 inches and 6 inches concrete slabs.
However, the required thickness depends mostly on the load factor. How much load you are going to put on the concrete is a key factor to determine the thickness of the slab required.
For example, general floor concrete in the residential spaces is 4 inches thick. But in outdoor concrete patios, driveways or parking require 6 inches thick slab where heavy trucks can move sometimes.
For heavier machinery than a garbage truck or an oil tanker, you will need thicker concrete than 6 inches.
However, the thickness of the concrete slab can't withstand even ordinary residential wear and tears if the base preparation, proper alignment, and mixing are not done correctly. So, for durable concrete construction, you need a combination of a thick and properly mixed concrete layer on top of a solid base.
Another key thing to consider is cured concrete thickness. When concrete cures, it shrinks a little bit. So, for pinpoint accuracy in thickness, it is required to make the wet concrete around 2% thicker than what you expect it to be after the curation process.
How Much is A Bag of Concrete?
Concrete bag prices vary depending on the materials in it, additives usage, drying time, strength, and the size of the bag.
A standard bag of cement weighing 60 lbs costs around 3.5 to 4 bucks while an 80 lbs bag costs 4.5 to 6 USD.
However, if you go with a quick setting or high strength additive-rich concrete mixer, a bag may cost you from 10 to a whopping 30 USD. These additive based concrete bags are made for concrete patching or repair so that they stick to the surface well.
However, some concrete mixture is also made for resurfacing concrete as well. Those mixtures are thinner and come with finishing materials in it so that you get shiny surface after application.
How Much Concrete Do I Need for Footing?
The calculation for the concrete footing is exactly the same as the general calculation we have discussed throughout this article. But people find it difficult to correctly estimate the footing concrete for a different reason.
When you pour concrete for the floor slabs, there remains a supporting base to hold the concrete. You get a perfect cube of a concrete surface according to your estimation.
But in footing, you pour the concrete on loose soil or sand surface. In most of the cases, the surface is uneven and gets suppressed because of the weight of the concrete. Concrete gets into the holes and pores to compensate the loose soil and you see the estimation exceeded by significant volume.
That's why we recommend inspecting the soil condition underneath the foundation, and getting 20 to 30% more bagged concrete to do a perfect job.
How Much Concrete Do I need for Concrete Steps?
The estimation of the volume for concrete steps is a bit tricky. You need to follow some steps to get into the result.
- Divide every step into rectangles.
- Measure the height, width, and depth of every rectangle.
- Add all the height measurements, widths, and depth measurements.
- Multiply the total height with total widths and total depths to get the total concrete volume.
How to Calculate Round Shaped Concrete?
When you need to make a round-shaped concrete block, round hole, or a ground post, you can't calculate the volume following the traditional way.
The calculation for round concrete surfaces is- π × radius × radius × depth.
For example, if you need to fill a round post hole with fast setting concrete, depth of which is 24 inches, the radius is 5 inch, then the calculation will be - 3.14159265359 × 5 × 5 × 24
So, the total volume of concrete needed for this is 1885 cubic inches.
Concrete budgeting is a crucial primary step before you call the ready mix supplier to come and pour concrete.
Keep in mind that the estimation won't be 100% accurate as there will be some losses in shipment, preparation, and application. The estimation is for getting an overall idea about the number of concrete bags you need and how much money you will end up spending on the project.
Although we have tried to cover almost all the relevant topics, if anything remains answered, feel free to leave a comment.