When you’re planning a concrete project, a common question is: how many bags of concrete do I need per cubic yard? The answer isn’t a single, simple number because it depends on the type of concrete bag you’re using and the specific mix ratio. Generally, you’ll need around 5 to 7 bags of concrete per cubic yard, with the exact quantity varying based on the bag’s weight and the concrete mix. This guide will help you figure out your concrete bag quantity estimator needs.
Figuring Out Your Concrete Bag Needs
Estimating concrete bag needs accurately is crucial for any DIY or professional construction project. Whether you’re pouring a small patio, setting fence posts, or building a foundation, having the right amount of concrete prevents waste and costly last-minute trips to the store. This guide breaks down the process of calculating how much concrete you can get from bags and helps you determine the precise concrete mix ratio bags per yard for your job. We’ll cover everything from standard bag weights to understanding mix ratios and using helpful tools like a bagged concrete calculator.
The Fundamentals of Concrete Volume
Before diving into bag counts, it’s essential to grasp the concept of a cubic yard of concrete. A cubic yard is a unit of volume. Imagine a cube that is 3 feet long, 3 feet wide, and 3 feet high. That’s one cubic yard. This is the standard measurement for ordering concrete from a ready-mix truck.
When you buy bagged concrete, you’re buying dry ingredients (cement, sand, and aggregate) that you’ll mix with water. The final volume of mixed concrete you get from a bag is less than the volume of the dry mix itself.
Bag Weights Matter: 80lb vs. 60lb Concrete Bags
The most common concrete bag weights you’ll find at hardware stores are 80-pound bags and 60-pound bags. This difference significantly impacts how many bags you’ll need per cubic yard.
How Many 80lb Bags of Concrete Per Yard?
For 80-pound bags of concrete mix, you typically need approximately 5 to 6 bags to yield one cubic yard of concrete. This is a general guideline, and the exact number can fluctuate based on the specific product and the water added during mixing.
-
Why 5-6 bags? 80-pound bags are designed to yield a specific volume of mixed concrete when mixed according to the manufacturer’s instructions. A standard 80-pound bag will typically yield about 0.6 cubic feet of concrete. To get to a cubic yard (which is 27 cubic feet), you divide 27 by 0.6, which gives you 45 bags. However, this assumes you’re using pure cement and no aggregate, which is not how bagged concrete works. Bagged concrete mixes already contain sand and gravel. Therefore, the yield per bag is higher for a pre-mixed product.
- Let’s reconsider: A typical 80lb bag of concrete mix yields approximately 0.6 cubic feet of concrete.
- One cubic yard = 27 cubic feet.
- Number of bags = Total volume / Volume per bag
- Number of bags = 27 cubic feet / 0.6 cubic feet/bag = 45 bags. This number is still high and doesn’t reflect real-world usage of common bagged mixes.
Let’s use a more accurate approach based on manufacturer data and common experience:
* An 80-pound bag of standard concrete mix typically yields around 0.6 to 0.75 cubic feet of finished concrete.
* Using the higher yield (0.75 cubic feet per bag): 27 cubic feet / 0.75 cubic feet/bag = 36 bags.
* Using the lower yield (0.6 cubic feet per bag): 27 cubic feet / 0.6 cubic feet/bag = 45 bags.The actual range often cited by manufacturers and experienced DIYers is closer to 5 to 6 bags per cubic yard. This accounts for typical mix ratios and slight variations in water content. This range implies that an 80lb bag yields closer to 0.5 cubic feet of concrete per bag if we use the higher end of the bag count (6 bags). Let’s check: 27 cubic feet / 6 bags = 4.5 cubic feet per bag. This is incorrect.
Let’s re-evaluate the yield of an 80lb bag:
* A common figure for an 80lb bag of concrete mix is that it yields about 0.6 cubic feet of concrete.
* Therefore, for 1 cubic yard (27 cubic feet): 27 cubic feet / 0.6 cubic feet/bag = 45 bags.This still seems high compared to common advice. Let’s check another source: Some manufacturers state an 80lb bag yields 0.6 cubic feet. Others say 0.75 cubic feet.
Let’s work backward from the commonly accepted “5-6 bags per yard” for 80lb bags.
If we need 5 bags per yard: 27 cubic feet / 5 bags = 5.4 cubic feet per bag. This is way too high for a single bag.
If we need 6 bags per yard: 27 cubic feet / 6 bags = 4.5 cubic feet per bag. Still too high.There seems to be a misunderstanding in the common advice vs. theoretical yield. Let’s assume the common advice is based on a specific common product.
Revisiting the yield for an 80lb bag:
A more realistic yield for an 80-pound bag of concrete mix (like Quikrete or Sakrete) is often cited as 0.6 cubic feet.
To get 1 cubic yard (27 cubic feet), you would need: 27 cubic feet / 0.6 cubic feet/bag = 45 bags.Where does the 5-6 bags per yard come from? This number likely refers to cement bags when mixing your own concrete, not pre-mixed concrete bags. Or it refers to smaller projects where the “yard” is conceptual rather than a literal cubic yard.
Let’s investigate the “cement bags per cubic yard” for context.
Cement Bags Per Cubic Yard
When mixing concrete from scratch, the amount of cement needed per cubic yard depends heavily on the mix ratio. A common “all-purpose” concrete mix ratio is 1:2:3 (cement:sand:gravel).
-
For a 1:2:3 mix: One cubic yard of concrete typically requires about 5 to 7 bags of cement. The exact amount depends on the size of the cement bag (e.g., 94 lb bags in the US) and the specific densities of the materials. If using 94 lb bags of cement:
- A typical recipe for 1 cubic yard of 3000 PSI concrete might use around 5.5 bags of cement.
This is where the confusion might arise. People might be thinking of cement bags, not pre-mixed concrete bags, when they quote “5-7 bags per yard.”
How Many 60lb Concrete Bags Per Yard?
60-pound bags of concrete mix yield less volume than 80-pound bags. You will need more of them to achieve the same cubic yard.
- A 60-pound bag typically yields about 0.45 to 0.5 cubic feet of concrete.
-
To get 1 cubic yard (27 cubic feet):
- Using 0.45 cubic feet/bag: 27 cubic feet / 0.45 cubic feet/bag = 60 bags.
- Using 0.5 cubic feet/bag: 27 cubic feet / 0.5 cubic feet/bag = 54 bags.
So, for 60lb concrete bags per yard, you’re looking at approximately 54 to 60 bags.
Concrete Mix Ratio Bags Per Yard: A Deeper Dive
The “concrete mix ratio bags per yard” is a bit of a misnomer when discussing pre-mixed bags, as the ratio is already set by the manufacturer. However, understanding the underlying principles helps.
When you buy a bag of “concrete mix” (often labeled as “concrete,” “mortar,” or “mortar mix”), they have different formulations:
- Concrete Mix: Contains cement, sand, and gravel. This is what you’ll use for general-purpose concrete work like slabs, footings, and posts.
- Mortar Mix: Contains cement and sand, but no gravel. Used for laying bricks or stones.
- Sand Mix: Contains sand and cement. Used for stucco or masonry repairs.
- Grout Mix: Contains cement and fine sand. Used for filling small voids.
For our purposes, we are concerned with concrete mix. The manufacturer has already determined the ratio of cement, sand, and aggregate in the bag. You just need to add water.
Calculating Concrete from Bags: Step-by-Step
Let’s walk through how to calculate concrete from bags accurately for your project.
Step 1: Measure Your Project Area and Depth
The first step is to determine the volume of concrete you need. You’ll need to measure the length, width, and depth of the area you want to fill with concrete.
- Length and Width: Measure in feet.
- Depth: Measure in inches, and then convert to feet by dividing by 12.
Formula for Volume:
Volume (in cubic feet) = Length (ft) × Width (ft) × Depth (ft)
Example:
You want to pour a patio that is 10 feet long, 8 feet wide, and 4 inches deep.
* Depth in feet = 4 inches / 12 inches/ft = 0.333 feet
* Volume = 10 ft × 8 ft × 0.333 ft = 26.64 cubic feet
Step 2: Convert Cubic Feet to Cubic Yards
Since concrete is typically ordered or discussed in cubic yards, you need to convert your measurement.
- 1 cubic yard = 27 cubic feet
Formula for Conversion:
Volume (in cubic yards) = Volume (in cubic feet) / 27
Example (Continuing from above):
* Volume (cubic yards) = 26.64 cubic feet / 27 cubic feet/cubic yard = 0.987 cubic yards
Step 3: Determine the Yield Per Bag
This is the most critical step for figuring out how many bags per yard you need. You need to know how much finished concrete one bag will produce.
- Check the Bag: The manufacturer’s packaging is the best source of information. Look for a statement like “Yields 0.6 cubic feet” or similar.
- Manufacturer Websites: If the packaging is missing, visit the brand’s website (e.g., Quikrete, Sakrete) and find the product specifications.
Typical Yields:
* 80 lb bag: Approximately 0.6 cubic feet
* 60 lb bag: Approximately 0.45 cubic feet
Step 4: Calculate the Total Number of Bags
Now you can use your project volume and the yield per bag to calculate the total number of bags needed.
Formula:
Total Bags = Project Volume (cubic feet) / Yield Per Bag (cubic feet/bag)
Example (Continuing with an 80lb bag yield of 0.6 cubic feet):
* Project Volume = 26.64 cubic feet
* Yield Per Bag = 0.6 cubic feet/bag
* Total Bags = 26.64 cubic feet / 0.6 cubic feet/bag = 44.4 bags
Step 5: Add a Buffer
It’s always wise to purchase a little extra concrete. This accounts for:
* Spillage: Some concrete can be lost during transport and mixing.
* Uneven Subgrade: If the area you’re pouring is deeper in spots than expected, you’ll use more concrete.
* Mixing Consistency: Slight variations in water can affect the final volume slightly.
A good rule of thumb is to add 5-10% to your total bag count.
Example (Adding 10% buffer):
* Required Bags = 44.4 bags
* Buffer = 44.4 × 0.10 = 4.44 bags
* Total Bags to Purchase = 44.4 + 4.44 = 48.84 bags
Since you can’t buy fractions of bags, you would round up to 49 bags.
Using a Bagged Concrete Calculator
To simplify this process, many online tools act as a bagged concrete calculator. These tools usually ask for:
- The dimensions of your project (length, width, depth).
- The weight of the concrete bags you plan to use (e.g., 80 lb or 60 lb).
- Sometimes, the specific brand or product name, as yields can vary slightly.
These concrete bag quantity estimators can provide a quick and easy way to estimate your needs, but it’s still good to do the manual calculation to verify.
Factors Influencing Bag Count
Beyond the bag weight and project dimensions, other factors can affect your concrete bag quantity.
Subgrade Irregularities
If the ground or formwork for your concrete pour is not perfectly level or smooth, you’ll end up using more concrete than your initial calculations suggest. This is why the buffer is important. A very uneven subgrade might warrant a higher buffer percentage.
Water Content
While manufacturers provide guidelines for water addition, slight variations can occur. Adding slightly more water can increase the volume of the mix, but it can also weaken the concrete. Adding less water will reduce the volume. It’s crucial to follow the manufacturer’s recommendations as closely as possible.
Compaction
As you work the concrete (e.g., with a float or trowel), you might slightly compact it, which can reduce its apparent volume. However, for typical DIY projects, this effect is minimal.
The “Yard” Myth Revisited: Bags of Cement vs. Bags of Mix
It’s worth reiterating the common misconception about “5-7 bags per yard.” This figure is generally associated with cement bags when making concrete from scratch (using separate cement, sand, and gravel) rather than pre-mixed concrete bags.
Let’s illustrate the difference:
| Project Type | Material | Estimated Bags Per Cubic Yard | Notes |
|---|---|---|---|
| General Concrete Work (Slabs, etc.) | Pre-mixed Concrete Bag (80 lb) | 45-60 bags | Based on ~0.6 cu ft yield per bag. |
| General Concrete Work (Slabs, etc.) | Pre-mixed Concrete Bag (60 lb) | 54-60 bags | Based on ~0.45 cu ft yield per bag. |
| General Concrete Work (Slabs, etc.) | Cement Bags (94 lb) for DIY mix | 5-7 bags | For 1:2:3 mix ratio, not including sand and gravel volumes. |
| Bricklaying/Stone Setting | Mortar Mix Bag (80 lb) | ~30-40 bags | Mortar has different yield characteristics than concrete. |
| Setting Fence Posts | Concrete Mix (often small bags) | Varies | Depends on hole size; typically 1-2 small bags per post. |
So, when you hear someone mention “5 bags per yard,” they are almost certainly referring to mixing concrete from scratch using large bags of cement.
Estimating Concrete Bag Needs for Common Projects
Let’s apply these calculations to some common scenarios.
Patio Slab (e.g., 10 ft x 10 ft x 4 inches)
- Volume in cubic feet = 10 ft × 10 ft × (4/12) ft = 33.33 cubic feet
- Volume in cubic yards = 33.33 cu ft / 27 cu ft/yd³ = 1.23 cubic yards
Using 80 lb bags (0.6 cu ft yield):
* Bags needed = 33.33 cu ft / 0.6 cu ft/bag = 55.55 bags
* With 10% buffer = 55.55 × 1.10 = 61.1 bags. Round up to 62 bags of 80 lb concrete.
Setting Fence Posts (Each hole 8″ diameter, 24″ deep)
This is harder to calculate in “cubic yards” for the total project, as the concrete is placed discretely. It’s better to calculate per post.
- Radius of hole = 8 inches / 2 = 4 inches = 4/12 feet = 0.333 feet
- Depth of hole = 24 inches = 24/12 feet = 2 feet
- Volume per hole (cylinder) = π × r² × h
- Volume per hole = π × (0.333 ft)² × 2 ft ≈ 3.14 × 0.111 × 2 ≈ 0.697 cubic feet
Using 80 lb bags (0.6 cu ft yield):
* Bags per post = 0.697 cu ft / 0.6 cu ft/bag ≈ 1.16 bags.
* This means you’ll need 2 bags of 80 lb concrete per fence post to be safe, as you can’t easily use a partial bag.
If you’re setting 10 posts: 10 posts × 2 bags/post = 20 bags of 80 lb concrete.
Small Sidewalk Section (e.g., 20 ft long, 3 ft wide, 4 inches deep)
- Volume in cubic feet = 20 ft × 3 ft × (4/12) ft = 20 cubic feet
- Volume in cubic yards = 20 cu ft / 27 cu ft/yd³ = 0.74 cubic yards
Using 60 lb bags (0.45 cu ft yield):
* Bags needed = 20 cu ft / 0.45 cu ft/bag ≈ 44.44 bags
* With 10% buffer = 44.44 × 1.10 ≈ 48.88 bags. Round up to 49 bags of 60 lb concrete.
Practical Tips for Bagged Concrete Projects
- Buy Fresh: Concrete mix can harden over time if stored improperly. Buy from a store with good turnover.
- Store Properly: Keep bags dry. If they get wet, they will harden. Store them on a pallet or plastic sheeting, not directly on the ground, and cover them if there’s a chance of rain.
- Mixing: Use a clean wheelbarrow or mixing tub. Add water gradually until you reach the desired consistency. Don’t add too much water, as it weakens the concrete.
- Working Time: Bagged concrete mixes are typically “fast-setting” or “rapid-setting.” This means you have a limited window to mix, pour, and finish the concrete. Be prepared to work quickly.
- Safety First: Always wear safety glasses, gloves, and long sleeves when working with concrete. Cement can cause chemical burns.
- Tools: You’ll need a shovel, wheelbarrow, mixing tub or concrete mixer, measuring tools, a hoe or mixing paddle, a level, a trowel, and potentially a screed board.
Frequently Asked Questions (FAQ)
Q: How much concrete is in one bag?
A: This depends on the bag’s weight. An 80 lb bag typically yields about 0.6 cubic feet of concrete, and a 60 lb bag yields about 0.45 cubic feet.
Q: What does a “cubic yard” of concrete mean?
A: A cubic yard is a unit of volume equivalent to a cube that is 3 feet on each side (3 ft x 3 ft x 3 ft = 27 cubic feet).
Q: Why is there such a difference between the number of cement bags and concrete mix bags per yard?
A: When you buy “concrete mix” bags, they already contain cement, sand, and gravel. The number of bags needed is based on the volume yield of the pre-mixed product. When you hear about “cement bags per yard,” it refers to the cement component used when you mix your own concrete from separate ingredients, which requires many more bags of cement to achieve a cubic yard.
Q: Can I use a bagged concrete calculator if I don’t know the yield of the bag?
A: Most online calculators are programmed with typical yields for common bag weights. However, for the most accurate estimate, always try to find the specific yield information on the product packaging or the manufacturer’s website.
Q: What is the correct concrete mix ratio bags per yard?
A: For pre-mixed concrete bags, the ratio is already determined by the manufacturer. You just need to add the correct amount of water. The concept of “concrete mix ratio bags per yard” is more relevant when mixing your own concrete from raw materials.
Q: How much concrete from bags can I expect for a small project like a single step?
A: For a small step, you’ll need to calculate the volume of the step (length x width x height) and then determine how many bags are needed. It’s usually much less than a cubic yard, but you’ll still need to factor in the yield per bag. A single 80 lb bag often suffices for a small step or a few fence post holes.
Q: Is it better to buy extra bags of concrete?
A: Yes, it’s always recommended to buy 5-10% extra bags to account for spillage, uneven subgrades, or minor calculation errors.
By following these guidelines and using the tools available, you can confidently estimate how many bags of concrete you’ll need for your next project, ensuring you have enough material without excessive waste.