Cubic Feet Per Bag of Concrete Explained for Beginners

When we are working on a small home renovation, we usually use bagged concrete. We buy multiple bags because we actually don’t know anything about the quantity of material or the bag size. We either buy it by guessing or following our contractor blindly. 

What happens next is, sometimes a lot of material goes wasted, and sometimes, we feel short on the material. This is why, whenever anyone starts such work, they should know the exact quantity of material that is needed for this project. 

Building a backyard concrete slab for a walkway or a small shade, these are small renovation works that people choose to do on their own. As such, they have one question in mind.

How many bags of concrete do we need for this? 

To know this, the first thing to know is the cubic feet per bag of concrete. Each pre-mixed bag of concrete gives a fixed yield. Every size bag gives a different quantity. 

A standard concrete bag, which is mostly an “80 lb bag” of premixed concrete, normally provides about 0.6 cubic feet of ready-mixed concrete. 

In the same way,  A 60 lb bag gives 0.45 cubic feet

A 40 lb bag gives about 0.3 cubic feet of mixed concrete

These are according to common manufacturer data in the U.S.

On the other hand, if you are working on a standard-sized thickness of concrete, you will need 0.33 cubic feet of concrete per square foot of area. 

Here, you can understand that sometimes, the work cannot be completed using one bag, and multiple bags are needed to cover the area fully.

These are some basic calculations and number games when you are working on a project involving concrete. 

So, let us tell you more about this. 

Understanding Cubic Feet Per Bag of Concrete

Cubic feet per bag of concrete means how much mixed concrete volume you get from one bag. A concrete bag is also known as a pre-mixed concrete bag, which contains a raw or dry form of concrete that becomes ready when wet. 

 

When you add water to a dry premixed concrete bag of any size from 40 pounds to 90 pounds, as available in your area,  it does not stay in “pounds” anymore. It turns into wet concrete that takes up space, and that space is measured in cubic feet. This value is necessary to understand how much area or volume one bag can fill in your project.

 

In the U.S., most premixed concrete bags follow similar yield ranges for every type of concrete.

 

90 lb bag = 0.7 cubic feet

80 lb bag = 0.6 cubic feet

60 lb bag = 0.45 cubic feet

40 lb bag = 0.3 cubic feet

 

This is shown in common bag charts from leading brands such as Quikrete and Sakrete. These numbers stay relatively standard, so you can safely use them while planning your project and the number of bags you need.

 

This “cubic feet per bag” weight becomes important when you connect it with your slab or footing size. 

 

You can understand it from this example: a 4-inch thick slab is built using about 0.33 cubic feet of concrete per square foot of area. 

 

Now, if one 80 lb bag gives 0.6 cubic feet, here you will understand that a single bag will not cover 0.33 cubic feet of space, which is four times thick. So, you will need multiple bags, but how many? For this, you will multiply the bags to know how many bags you actually need. 

 

This is why it is important to know the cubic feet per bag of concrete. This knowledge will let you match your project’s concrete volume with the correct number of bags required. What happens next is that you will avoid running short or overbuying, which will become nothing but waste.

How to Calculate the Bags of Concrete You Need

If you know the volume of concrete for your project and the cubic feet per bag, then you can calculate the quantity of concrete bags you need.

 

One of the simplest steps in calculating the concrete volume accurately and fastly is the use of a Concrete Calculator.  A calculator can tell you exactly how much concrete you need based on your area measurements and slab thickness.

 

It requires a few inputs from you, which are based on the working area dimension, and in return, it gives you the outputs showing how much concrete you need. The outputs are in cubic feet, cubic yards,  and also the number of bags. This estimate by the calculator gives you a rough idea of the concrete bags you need to buy for your work. 

 

You can also calculate it manually, and for this, you should first measure the length, width, and thickness of the area you want to work on. Then, multiply these three measurements to get the total volume. Make sure you use the “feet” unit for all three to get the answer in cubic feet.

 

The next step is you should check the cubic feet per bag for the type and size of bag you are using. You can get this information from the outer cover of the concrete bag. After this, you will have to use and divide your total volume by the cubic feet per bag to find the number of bags required.

 

Moreover, whenever calculating the concrete volume, do not calculate with the exact estimate, but include a little margin and add five or ten percent extra to the total volume you get. 

 

Here is a small sample example for your understanding

 

Just take the area: 10 ft × 10 ft, 4-inch or 0.33 ft thick 

 

So the concrete volume you get is 33 cubic feet from 10 × 10 × 0.33 

 

If you are intending to buy an 80 lb bag for this work, you should know how much concrete you will get from one bag and how much you will need to cover the area of 33 cubic feet. 

 

One 80 lb bag = 0.6 cubic feet

The area you want to cover =  33 cubic feet. 

 

You will have to find out how many bags you need. So for this,

 

 33 ÷ 0.6 = 55 bags

 

Add 5% extra, and this will be 55 × 1.05 = 58 bags

 

Here, you will get the answer that you should buy a minimum of 58 bags to fill the area of 33 cubic feet. 

Bag Size vs Project Type

The selection of the right bag size depends on the type and size of the area you are working on. If you are working on minor changes or renovation works on your own then the best recommendation is to buy smaller sized bags like 40lb bags. 

 

These size bags are a good option for minor construction works like fence posts or patching work. Another benefit of buying this is that the bags of this size are easier to carry and mix. Moreover, the concrete will be utilized in full amount and no material will be wasted.

 

Another option is medium sized bags, like a 60 lb bag of concrete. These are medium sized and are a suitable option for medium-sized slabs, garden paths, or decks. This is a good size and a balanced option where you need more than one 40 lb bag and less than two. You can buy one 60 lb bag at this stage. These bags are also easy to handle and also reduce the effort to carry multiple small bags.

 

In larger projects like full driveway slabs or garage floors, and also for commercial work, 80 lb or 90 lb bags are a more suitable option. A bigger bag has more concrete, so this way less bags are needed. Mixing and spreading the concrete in larger amounts also becomes quicker for bigger areas.

 

So, you will have to match the bag size to your project type. In return, you will avail a number of benefits. 

 

• You will save time
• You will participate in reducing concrete waste 
• The project will be handled and managed easily when the material is available

 

So, use a concrete calculator along with the right bag size so you can order the correct amount of concrete for your specific project.

Why a Concrete Bag Calculator Is a Good Tool

A concrete bag calculator is a great tool when you are working on a concrete project. It eases the planning of your construction material and budget. When you are using the digital tool, you don’t need to estimate by eye; you can enter your area dimensions and bag size, and the calculator will instantly tell you how many bags you need.

 

It saves time and reduces stress by doing all the calculations for you, including conversions from square feet to cubic feet or cubic yards. This way, you can prevent waste and order only the required and necessary amount of concrete you need. This means no extra cost, no material wastage, and no leftover material.

 

For both beginners and experienced, a concrete bag calculator is a necessary tool that makes the project go within the estimated budget and is planned according to the material.

Case Study on Optimizing Concrete Bag Usage in a Residential Project

A 2022 project by Quikrete, a leading concrete manufacturer in the U.S., studied many types of residential slab pours using pre-mixed concrete bags. 

 

The project team tracked over-ordering and waste when homeowners manually estimated bags versus using a concrete calculator.

 

The results showed that projects using a calculator to match bag size with project volume reduced concrete bag waste by up to 15%. 

 

For example, a 10 ft × 12 ft, 4-inch thick patio required around 55 bags of 80 lb concrete when estimated manually, but the calculator suggested 50 bags, saving 5 bags worth of material and cost.

 

This explained how the knowledge of cubic feet per bag and proper estimation with a concrete calculator can help everyone to save a lot in their work. 

Final Words 

What does a concrete project need for finalization?
Indeed, it is the right amount of material so that the project could end up with ease and proper finalization all at once. A concrete bag calculator has proven to be a successful tool in such projects. 

 

When you know the cubic feet per bag and match it to your project, your work is planned better, and you can avail several benefits from accurate calculation.

 

So, take the time to measure and calculate with the help of the calculator to finalize your project in a better way.

Frequently Asked Questions 

How many 80lb bags of concrete do I need for 1 cubic foot?

You need two bags of 80 lbs for 1 cubic foot. One bag gives 0.6 cubic feet of mixed concrete.  

Is it cheaper to mix your own concrete or buy bags?

It is cheaper to buy bags for small scale projects because it is a convenient and reasonable option. On the other hand, mixing your own concrete from bulk materials is a cheaper option in larger projects. 

How many cubic feet are in a 60 lb bag of concrete?

0.45 cubic feet are in a 60 lb concrete bag.