Here is a detailed blog post about calculating how many 80# bags of concrete are in a yard.
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Calculating How Many 80# Bags Of Concrete In A Yard
How many 80# bags of concrete do you need for a cubic yard? You will need about 45 bags of 80-pound concrete mix to make one cubic yard of concrete. This number helps when you are figuring out how much concrete needed for your project. Knowing the approximate number helps you plan and buy the right amount of material.
Grasping the Idea of a Cubic Yard
When we talk about concrete, especially for bigger jobs like patios or footings, the amount is often measured in cubic yards.
h5 What is a Cubic Yard?
Picture a box that is 3 feet long, 3 feet wide, and 3 feet tall. The amount of space inside that box is one cubic yard. This is the standard measure for concrete volume on many construction sites.
h5 Cubic Feet in a Cubic Yard
To figure out how many bags you need, it helps to think in smaller steps. A cubic foot is a box that is 1 foot long, 1 foot wide, and 1 foot tall. How many of these small cubic foot boxes fit inside the big cubic yard box?
You multiply the length, width, and height in feet:
3 feet * 3 feet * 3 feet = 27 cubic feet.
So, one cubic yard is the same as 27 cubic feet. Knowing how many cubic feet in a yard of concrete is key to figuring out bags.
Deciphering Concrete Bags
Concrete comes in bags. Bags are sold by weight, like 80 pounds (#), 60 pounds, or 40 pounds. But when you mix the concrete, it takes up space, which is a volume.
h5 Concrete Yield Per Bag
Each bag of concrete mix, when mixed with the right amount of water, will produce a certain amount of wet concrete. This amount is called the “yield.” The yield is the volume of concrete you get from one bag.
The yield depends on the size of the bag.
* An 80# bag of concrete mix typically yields about 0.6 cubic feet of mixed concrete.
* A 60# bag typically yields about 0.45 cubic feet of mixed concrete.
* A 40# bag typically yields about 0.3 cubic feet of mixed concrete.
These numbers are averages. The actual volume of concrete bags can change a little based on how much water you add and how well you mix it. But using these typical yield numbers is the standard way to estimate.
The Main Calculation: Bags Needed for a Yard
Now we have the two key numbers:
1. One cubic yard is 27 cubic feet.
2. One 80# bag of concrete mix yields about 0.6 cubic feet.
To find out how many 80# bags are in one cubic yard, you divide the total volume you need (in cubic feet) by the volume one bag makes (in cubic feet).
h5 Doing the Cubic Yard Concrete Calculation
For one cubic yard:
* Total volume needed = 27 cubic feet
* Yield per 80# bag = 0.6 cubic feet
Number of 80# bags = Total volume needed / Yield per bag
Number of 80# bags = 27 cubic feet / 0.6 cubic feet per bag
Let’s do the math:
27 / 0.6 = 45
This shows you need about 45 of the 80-pound bags of concrete mix to make one cubic yard. This is the basic cubic yard concrete calculation for 80lb bags.
Why It’s “About” 45 Bags
It is important to remember that 45 bags is an estimate. The real yield from a bag can change a little.
h5 Factors that Change Bag Yield
- How much water you add: Adding too much water makes the concrete weaker and can slightly increase the volume, but this is not a good practice for strong concrete. Using the right amount gives the best result and the expected yield.
- How well you mix: Mixing completely makes sure you get all the concrete material into the mix. Poor mixing can leave some material unused, slightly changing the yield.
- Batch differences: Even bags of the same type can have tiny differences from one batch to another at the factory.
- Waste: Some concrete mix might be spilled during mixing or placing. This means you might use a bit more mix than the pure calculation suggests.
Because of these things, the calculation is always an estimate. It tells you a very close number to plan with.
Converting Cubic Yards to Bags of Concrete: Other Bag Sizes
Concrete mix comes in different bag sizes. The process for figuring out how many bags you need for a cubic yard is the same, but you use the yield for that specific bag size. This is how you do converting cubic yards to bags concrete for any size.
h5 Number of 60lb Bags Per Yard
A common bag size is 60 pounds.
* Yield per 60# bag = about 0.45 cubic feet.
* Total volume needed for a yard = 27 cubic feet.
Number of 60# bags = Total volume needed / Yield per bag
Number of 60# bags = 27 cubic feet / 0.45 cubic feet per bag
Let’s do the math:
27 / 0.45 = 60
You need about 60 of the 60-pound bags of concrete mix to make one cubic yard. So, the number of 60lb bags per yard is around 60.
h5 Number of 40lb Bags Per Yard
Another size is 40 pounds.
* Yield per 40# bag = about 0.3 cubic feet.
* Total volume needed for a yard = 27 cubic feet.
Number of 40# bags = Total volume needed / Yield per bag
Number of 40# bags = 27 cubic feet / 0.3 cubic feet per bag
Let’s do the math:
27 / 0.3 = 90
You need about 90 of the 40-pound bags of concrete mix to make one cubic yard.
h5 Table of Bag Yields and Bags Per Yard
Here is a quick look at how many bags of different sizes you need for one cubic yard based on typical yields:
| Bag Size (Weight) | Typical Yield (Cubic Feet) | Approximate Bags Per Cubic Yard (27 cu ft) |
|---|---|---|
| 80 pounds (#) | 0.6 cubic feet | 27 / 0.6 = 45 bags |
| 60 pounds (#) | 0.45 cubic feet | 27 / 0.45 = 60 bags |
| 40 pounds (#) | 0.3 cubic feet | 27 / 0.3 = 90 bags |
This table summarizes the relationship between bag size, yield, and how many bags make up a cubic yard.
Calculating Concrete for Your Project
Most of the time, you won’t need exactly one cubic yard. You will need enough concrete to fill a specific space, like a path, a post hole, or a slab. This is where figuring out how much concrete needed for your specific job comes in.
h5 Figuring Out Volume for Different Shapes
- Rectangles or Squares (like slabs, paths, footings):
- Measure the length, width, and thickness of the area you need to fill.
- Make sure all your measurements are in the same unit, usually feet. If you measure thickness in inches (which is common for slabs), you need to change it to feet by dividing by 12.
- Multiply Length (in feet) * Width (in feet) * Thickness (in feet). This gives you the volume in cubic feet.
- Circles (like column bases):
- Measure the radius (half of the distance across the circle) in feet.
- Measure the height or thickness in feet.
- Volume = π (pi, about 3.14) * radius * radius * height.
- Cylinders (like sono tube footings):
- Measure the radius of the tube opening in feet.
- Measure the height of the tube in feet.
- Volume = π (pi, about 3.14) * radius * radius * height. (Same formula as a circle base, just thinking of height instead of thickness).
h5 Example: Estimating Concrete for Slab
Let’s say you want to pour a concrete slab for a small shed.
* The slab needs to be 10 feet long.
* It needs to be 8 feet wide.
* It needs to be 4 inches thick.
First, change the thickness to feet:
4 inches / 12 inches per foot = 0.333… feet (we can use 0.34 feet for easier math, or keep 4/12).
Now, calculate the volume in cubic feet:
Volume = Length * Width * Thickness
Volume = 10 feet * 8 feet * (4/12) feet
Volume = 80 * (1/3) cubic feet
Volume = 80 / 3 cubic feet
Volume = about 26.67 cubic feet
Now you know the total volume needed is about 26.67 cubic feet. This is the first step in estimating concrete for slab.
h5 Calculating Bags for the Slab
You know you need 26.67 cubic feet of concrete.
If you are using 80# bags (which yield about 0.6 cubic feet each):
Number of 80# bags = Total volume needed / Yield per bag
Number of 80# bags = 26.67 cubic feet / 0.6 cubic feet per bag
Let’s do the math:
26.67 / 0.6 = 44.45 bags
You cannot buy parts of a bag. So, you need to round up to the next whole bag. In this case, you would need 45 bags.
If you were using 60# bags (which yield about 0.45 cubic feet each):
Number of 60# bags = 26.67 cubic feet / 0.45 cubic feet per bag
Let’s do the math:
26.67 / 0.45 = 59.27 bags
Round up: You would need 60 bags.
This example shows you how to figure out how much concrete needed in bags for a specific project like a slab.
Getting a Handle on Waste and Ordering Extra
The calculations give you the exact amount of mixed concrete volume needed to fill the space. However, it’s wise to buy a little extra concrete mix.
h5 Why Buy Extra?
- Spillage: It’s easy to spill some mix when moving or pouring.
- Uneven Base: The ground or formwork might not be perfectly level, meaning you need a little more concrete to fill low spots.
- Mixing Errors: Sometimes a batch might be mixed incorrectly, making it unusable.
- Underestimation: Your measurements might be slightly off, or the yield per bag might be slightly less than expected.
Most people suggest adding 5% to 10% extra to your calculation.
h5 Adding a Waste Factor to Our Slab Example
For our 10x8x4 inch slab, we calculated we need about 45 of the 80# bags.
Let’s add 10% for waste:
Extra bags = 45 bags * 10% (or 0.10)
Extra bags = 4.5 bags
Total bags needed = Calculated bags + Extra bags
Total bags needed = 45 + 4.5 = 49.5 bags
Round up to the nearest whole bag: You should probably buy 50 bags of 80#.
This extra buffer helps make sure you don’t run out of concrete during the job. Running out means stopping work, going to the store, and mixing a small batch later, which can be hard to match perfectly. It is much better to have a bag or two left over.
Using a Concrete Bag Calculator
Doing the math each time can be a bit tedious, especially with unit conversions. Many websites and apps offer a concrete bag calculator.
h5 How Concrete Calculators Work
These online tools usually ask for:
* The shape of your project (slab, footing, column, etc.).
* The measurements (length, width, thickness, diameter, height) in your chosen units (feet, inches, meters).
* The size of the concrete bag you plan to use (40#, 60#, 80#).
You put in your numbers, and the calculator does the math for you. It figures out the volume in cubic feet or cubic yards and then divides by the typical yield of the bag size you picked. Some calculators even ask for a waste percentage and add that for you.
Using a concrete bag calculator is a fast way to get the number of bags you need, based on standard yield numbers. Just make sure the calculator uses the same yield numbers you expect, or allows you to enter the yield per bag.
Understanding the Weight of Concrete
We’ve focused on volume (how much space concrete fills) and bag weight (how bags are sold). But it is also useful to know the weight of a cubic yard of concrete. This helps you understand how heavy the material is you are working with.
h5 How Much Does Concrete Weigh?
Mixed concrete is very heavy. Its weight per cubic foot depends on what it is made of. Regular concrete, using common stone and sand, weighs about 150 pounds per cubic foot.
h5 Calculating Weight of a Cubic Yard
Since one cubic yard is 27 cubic feet, you can find the weight of a cubic yard:
Weight per cubic yard = Weight per cubic foot * Number of cubic feet in a yard
Weight per cubic yard = 150 pounds/cubic foot * 27 cubic feet
Let’s do the math:
150 * 27 = 4050 pounds
So, the weight of a cubic yard of concrete is about 4050 pounds. That’s over 2 tons! This is important to know when thinking about transporting mixed concrete or the weight of your finished structure.
Bags vs. Ready-Mix Concrete
For small jobs, buying bags of concrete mix and mixing them yourself is often the most practical way to go. It lets you mix only what you need, bit by bit.
However, for larger jobs, like pouring a big patio, a driveway, or footings for a house, mixing dozens or even hundreds of bags by hand (or even with a small mixer) is a lot of work.
For larger volumes, it is usually better to order ready-mix concrete. This comes premixed in a large truck and is poured directly into your forms. Ready-mix is ordered by the cubic yard.
h5 When to Choose Bags
- Small repairs
- Setting fence posts
- Pouring a small step or curbing
- Jobs needing less than 1 cubic yard (or maybe up to 2 yards if you have help and equipment)
h5 When to Choose Ready-Mix
- Pouring large slabs (patios, driveways, garage floors)
- Building foundations or large footings
- Any project needing more than 1.5 to 2 cubic yards, depending on your labor and equipment.
Knowing how many bags make a yard helps you compare the cost of buying many bags versus ordering a truck. It also helps you decide which method is best for your project size.
Reviewing the Process
Let’s quickly go over the steps to figure out how many 80# bags of concrete you need for a job:
- Figure out the volume needed: Measure the length, width, and thickness of the area you need to fill. Make sure all measurements are in feet. (Remember to divide inches by 12 to get feet). Multiply Length * Width * Thickness to get the volume in cubic feet. If your shape is not a simple rectangle, use the right volume formula.
- Pick your bag size: Decide if you will use 80#, 60#, or 40# bags.
- Find the yield per bag: Use the typical yield for your bag size (0.6 cu ft for 80#, 0.45 cu ft for 60#, 0.3 cu ft for 40#).
- Calculate the number of bags: Divide the total volume needed (in cubic feet) by the yield per bag (in cubic feet).
- Round up: You can only buy whole bags, so round your answer up to the next whole number.
- Add for waste: Add an extra 5% to 10% to your number of bags to be safe. Round up again if needed.
This process gives you a very good estimate for buying the right amount of concrete mix for your job.
Important Notes on Mixing
Getting the right yield and strength from your concrete bags depends on proper mixing.
h5 Tips for Mixing Bagged Concrete
- Read the bag: Always follow the instructions on the concrete bag for how much water to add. Too much water makes weak concrete.
- Mix thoroughly: Mix until the concrete is a consistent color and texture, with no dry spots.
- Use the right tools: For a few bags, a wheelbarrow and shovel work. For more bags, a small concrete mixer machine saves a lot of effort and helps mix better.
- Mix close to where you will pour: Wet concrete is very heavy and hard to move far.
Following these tips helps ensure you get the expected volume and strength from your concrete mix.
Frequently Asked Questions (FAQ)
h5 Is the yield of 0.6 cubic feet for an 80# bag always exact?
No, it is an average or typical yield. The actual volume can change slightly based on the exact mix design inside the bag, how much water is added, and how well it is mixed. Using 0.6 cubic feet is the standard way to estimate, but remember it is not a perfect number.
h5 Should I buy exactly the number of bags I calculate?
It is highly recommended to buy extra bags. Adding 5% to 10% for waste and potential underestimation is a good idea. It’s much better to have one or two bags left over than to run out in the middle of your project.
h5 Does the weight of the bag matter, or just the yield?
Both matter in different ways. The weight (80#, 60#, 40#) is how the bags are sold and tells you which yield number to use for your calculation (0.6, 0.45, or 0.3 cu ft). The total weight of the concrete you make (like the 4050 lbs per cubic yard) matters for planning how to handle and support the finished concrete. But for figuring out how many bags fill a space, the yield volume is the key number.
h5 How do I measure the thickness of a slab area accurately before pouring?
Use stakes or screed boards set to the exact height needed. Measure from the prepared base to the top of these guides. This ensures your calculation for thickness is correct before you order or mix any concrete.
h5 Can I mix different bag sizes together for a project?
Yes, you can, as long as they are the same type of concrete mix (like standard concrete mix, not mortar or sand mix). However, it can make calculating a bit more complex if you use a mix of 80#, 60#, and 40# bags for the same volume calculation. It is usually easier to just use one size bag for a project if possible.
h5 What is the difference between concrete mix, mortar mix, and sand mix?
These are different materials for different jobs.
* Concrete mix: Contains portland cement, sand, and gravel (small stones). Used for structural things like slabs, footings, and posts.
* Mortar mix: Contains portland cement, sand, and sometimes lime. Used for laying bricks, blocks, or stone. It does not have gravel.
* Sand mix: Contains portland cement and sand only. Used for topping slabs, leveling, or where thinner concrete is needed without large gravel.
Always make sure you are buying concrete mix for jobs that need concrete strength.
Wrapping Up
Knowing how many 80# bags of concrete are in a yard – about 45 bags – is a basic but important piece of information for anyone doing concrete work. It is the starting point for figuring out how much material you need for jobs of any size. By figuring out the volume of your project in cubic feet, dividing by the yield of the bag you choose (like 0.6 cu ft for an 80# bag), and adding a little extra for safety, you can buy the right amount of concrete mix, save money, and avoid the stress of running out during the job. Remember that this same method works for other bag sizes too, just use the correct yield number for that bag.