Concrete is a very common building material used in many construction projects. It is made by mixing cement, aggregate (such as sand and gravel), water, and sometimes other additives. When setting concrete, it is measured in terms of cubic yards, where 1 cubic yard (yd3) equals 27 cubic feet. Determining how many bags of concrete mix are needed to make 1 yard of concrete depends on the size and weight of the bags.
Quick Answer
For standard 80 lb bags of concrete mix, it takes approximately 45 bags to make 1 cubic yard of concrete.
Calculating Bags of Concrete Per Cubic Yard
To calculate how many bags of concrete are required per yard, the weight of the bags must be converted to cubic feet:
- 1 cubic foot of concrete weighs approximately 150 lbs
- An 80 lb bag of concrete occupies 80/150 = 0.533 cubic feet
- There are 27 cubic feet in 1 cubic yard
- So to make 1 cubic yard will require 27/0.533 = approximately 45 bags of 80 lb concrete
Therefore, if using standard 80 lb bags of concrete mix, it would take about 45 bags to yield 1 cubic yard of concrete.
Examples
Here are some examples to illustrate the math:
1 Cubic Yard Example
- 1 cubic yard = 27 cubic feet of concrete
- Each 80 lb bag yields 0.533 cubic feet
- 27 cubic feet / 0.533 cubic feet per bag = 50.66 bags
- Rounding up: 51 bags of 80 lb concrete mix per 1 cubic yard
Half Cubic Yard Example
- 0.5 cubic yard = 13.5 cubic feet of concrete
- Each 80 lb bag yields 0.533 cubic feet
- 13.5 cubic feet / 0.533 cubic feet per bag = 25.33 bags
- Rounding up: 26 bags of 80 lb concrete mix per half cubic yard
Factors Affecting Number of Bags
There are several factors that can affect the number of concrete bags needed per yard:
1. Bag Weight
The standard bag weight used is 80 lbs. However, bags may range from 40-80 lbs. The heavier the bags, the fewer needed per yard. For example:
- 60 lb bags: 75 bags per cubic yard
- 70 lb bags: 64 bags per cubic yard
- 80 lb bags: 45 bags per cubic yard
2. Concrete Density
The density of concrete by volume is considered 150 lbs per cubic foot. However, concrete density can vary from 140-155 lbs per cubic foot depending on the aggregate used. The higher the density, the more bags will be required.
3. Mix Design
Factors like water content, aggregate size, and additives can affect the yield of a bag of concrete. Concrete with smaller aggregate and less water will yield more volume per bag.
4. Compaction
Proper compaction and consolidation of poured concrete reduces air pockets and voids, increasing the density. The more tightly compacted the concrete is, the more volume it will yield per bag.
5. Waste
Some concrete will be wasted or left in bags, so accounting for waste factor will increase the number of bags needed. An extra 10% is commonly added.
Estimating Charts
Many concrete suppliers provide concrete estimating charts to simplify the process. For example, this handy reference chart shows number of bags needed based on project dimensions:
| Project Dimensions | Number of 80 lb bags needed |
|---|---|
| 4′ x 8′ x 4″ | 4 bags |
| 6′ x 6′ x 4″ | 6 bags |
| 8′ x 8′ x 4″ | 9 bags |
| 10′ x 10′ x 4″ | 14 bags |
| 12′ x 12′ x 4″ | 18 bags |
Rather than calculating exact volumes, these charts provide a simple rule of thumb for estimating based on the size of small projects.
Ordering Tips
When purchasing concrete, keep these tips in mind:
- Order 5-10% extra bags to allow for waste and overages
- Round up bag estimates to simplify ordering – better to have leftovers than run short
- Have extra bags delivered with the initial order to avoid paying multiple delivery fees
- Store any unopened extra bags properly until needed again
- Purchase concrete from the same source when doing multiple loads for color consistency
Things to Consider When Ordering Concrete
In addition to the number of bags, consider these other factors when purchasing concrete:
Concrete Type
Various concrete mixes are formulated for specific applications and curing times:
- General purpose -good for simple slabs, footings, and small projects
- High strength – used for structural elements like foundations and retaining walls
- Quick setting – hardens faster, good for projects needing fast turnaround
- Cold weather – formulated to cure properly in low temps
Aggregate Size
Aggregate comes in different sizes for different finishing techniques:
- Small aggregate – smoother finish for decorative concrete
- Large aggregate – rougher textures like exposed aggregate
Specialty Options
Admixtures can be added for specific properties:
- Fiber reinforcement – for added strength and crack resistance
- Integral color – colored concrete for decorative finishes
- Air entrainment – improves workability and freeze-thaw resistance
Delivery Method
Choose delivery based on project scope:
- Bagged – for small DIY projects. Load into truck or trailer.
- Bulk – pumped from truck for larger pours. Needs finishing skills.
Mixing Tips
Proper mixing technique is key to achieving optimal concrete strength and durability:
- Add water gradually – too much water weakens concrete
- Mix thoroughly for 2-3 minutes to properly integrate ingredients
- Don’t re-temper partially set concrete
- Follow safety precautions – wear gloves, goggles, dust mask
- Clean tools promptly before concrete hardens
Curing Tips
Proper concrete curing improves strength and durability:
- Wet cure for 1 week, keeping concrete moist by misting or wet burlap
- Cover surface with plastic sheeting to retain moisture
- Apply curing compounds according to manufacturer
- Control temperature to avoid freezing or overheating
- Protect from foot traffic until fully cured
Conclusion
When working with bagged concrete, it’s important to calculate the number of bags needed to yield one cubic yard of concrete. For standard 80 lb bags, approximately 45 bags are required per cubic yard. However, you must also consider the bag weight, concrete density, mix design, compaction, and waste factors when estimating. Supplier charts can provide good rule-of-thumb guidance. Remember to also factor in concrete type, aggregate size, specialty admixtures, and delivery method for your project. With proper mixing and curing techniques, you can achieve optimal strength and durability from your concrete project.
