Ordering concrete by the yard might seem straightforward, but it’s a process where details matter. The basic answer to “How much concrete do I need?” is found by calculating the volume of your project and converting it into cubic yards. This article will guide you through every step, ensuring you order the correct amount of concrete for your needs, avoid costly mistakes, and get the best value.
Figuring Out Your Concrete Needs: The Math Made Simple
Before you pick up the phone, you need to know exactly how much concrete your project requires. This is all about volume. Whether you’re pouring a patio, a sidewalk, or a foundation, you’ll be dealing with dimensions: length, width, and depth.
Calculating Volume: Length x Width x Depth
The fundamental formula for volume is consistent across most shapes. For simple rectangular or square areas, it’s a direct multiplication:
- Length: The longest dimension of your pour.
- Width: The shorter dimension of your pour.
- Depth (or Thickness): How thick the concrete needs to be.
Let’s say you’re pouring a rectangular patio that is 10 feet long, 8 feet wide, and 4 inches thick.
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Convert All Measurements to the Same Unit: Since concrete is ordered in cubic yards, it’s often easiest to work in feet.
- Length: 10 feet
- Width: 8 feet
- Depth: 4 inches needs to be converted to feet. There are 12 inches in a foot, so 4 inches / 12 inches/foot = 0.333 feet.
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Calculate the Volume in Cubic Feet:
- Volume (cubic feet) = Length × Width × Depth
- Volume = 10 ft × 8 ft × 0.333 ft = 26.64 cubic feet
Converting Cubic Feet to Cubic Yards
This is where the “by the yard” part comes in. A cubic yard is a cube that is 3 feet long, 3 feet wide, and 3 feet high. Therefore, there are 27 cubic feet in one cubic yard (3 ft × 3 ft × 3 ft = 27 cubic feet).
To convert your cubic feet measurement to cubic yards, divide by 27:
- Volume (cubic yards) = Volume (cubic feet) / 27
- Volume = 26.64 cubic feet / 27 cubic feet/cubic yard = 0.987 cubic yards
Practical Applications and Estimating
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Circular Slabs: For circular patios or columns, you’ll need the radius (half the diameter) and the depth. The formula for the volume of a cylinder is π * radius² * depth.
- Example: A circular patio 10 feet in diameter (5-foot radius) and 4 inches (0.333 ft) thick.
- Volume (cubic feet) = 3.14159 × (5 ft)² × 0.333 ft
- Volume = 3.14159 × 25 sq ft × 0.333 ft = 26.17 cubic feet
- Volume (cubic yards) = 26.17 cubic feet / 27 = 0.97 cubic yards
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Irregular Shapes: For more complex shapes, break them down into simpler geometric forms (rectangles, squares, triangles, circles) and calculate the volume of each part. Then add them together.
Using a Concrete Calculator
Many online resources offer a concrete calculator. These tools are invaluable. You simply input your project’s dimensions (length, width, depth), and the calculator does the math for you, often directly providing the volume of concrete in cubic yards. Some advanced calculators can even account for different pour shapes.
The Importance of Over-ordering: The 10% Rule
It is almost always recommended to order 10% more concrete than your calculated amount. Why?
- Uneven Subgrade: The ground beneath your pour might not be perfectly level. Low spots will require more concrete to fill.
- Spillage: Some concrete can be lost during the pour, especially when transferring from the concrete truck to the forms.
- Settlement: Concrete can settle slightly as it cures.
- Insufficient Quantity: Running out of concrete midway through a pour is a disaster. Stopping a pour mid-way creates a weak joint that can crack later. Having a little extra is far better than having too little.
So, for our patio example that calculated to 0.987 cubic yards, adding 10% would mean ordering:
- 0.987 cubic yards × 1.10 = 1.0857 cubic yards
Since concrete is typically ordered in quarter or half-yard increments, you would likely round up and order 1.25 cubic yards.
Choosing the Right Concrete Mix: Strength and Durability
Concrete isn’t a one-size-fits-all material. The concrete mix ratio is crucial for its strength, durability, and suitability for your specific application. This ratio refers to the proportion of cement, aggregates (sand and gravel), and water.
Understanding Concrete Strength (PSI)
Concrete strength is measured in pounds per square inch (PSI). Common PSI ratings for residential projects include:
- 2500 PSI: Often used for sidewalks, patios, and pathways.
- 3000 PSI: A very common mix for general-purpose use, foundations, and driveways.
- 3500-4000 PSI: Used for heavier-duty applications like garage slabs, reinforced foundations, and structural elements.
- 5000+ PSI: For significant structural loads and industrial applications.
Your contractor or building codes will often specify the required PSI.
Additives and Their Purpose
Beyond the basic ingredients, various admixtures can be added to modify the concrete’s properties:
- Air-Entraining Admixtures: Improve resistance to freeze-thaw cycles, making concrete more durable in colder climates. Essential for exterior pours in regions with winter weather.
- Water Reducers: Allow for a lower water-to-cement ratio, leading to stronger and more durable concrete without sacrificing workability.
- Accelerators: Speed up the setting time, useful in cold weather or when a quick turnaround is needed.
- Retarders: Slow down the setting time, beneficial in hot weather to prevent premature stiffening.
- Fibers (Steel or Synthetic): Added to reduce shrinkage cracking and increase tensile strength.
The Slump Test: Measuring Workability
The slump test is a standard method used by the concrete batch plant and at the job site to measure the consistency or workability of fresh concrete. It indicates how much the concrete will slump or settle under its own weight.
- High Slump: Means the concrete is very wet and easy to pour and work with, but may be weaker if the water content is too high.
- Low Slump: Means the concrete is stiff and harder to work with, but generally stronger.
The desired slump depends on the application. For example, a flat patio might need a slump of 4-5 inches, while a wall with a lot of rebar might require a lower slump (2-3 inches) to ensure it doesn’t slump out of the forms. When you order concrete, you might specify a desired slump, or the concrete batch plant will recommend one based on your project.
The Ordering Process: From Calculation to Delivery
Once you’ve determined the volume of concrete and the appropriate mix, it’s time to place your order.
Who to Call: Ready-Mix Concrete Suppliers
You’ll be contacting ordering ready-mix concrete suppliers. These companies operate concrete batch plants where concrete is mixed according to specific orders and then transported to your job site in concrete trucks.
What Information to Provide When Ordering
When you call to order, be prepared to provide the following details:
- Your Location: The exact delivery address, including any access restrictions for large trucks.
- Quantity: The exact cubic yard of concrete you need, plus the 10% overage.
- Concrete Mix Design:
- PSI Strength: (e.g., 3000 PSI)
- Aggregate Size: The maximum size of the gravel in the mix. Common sizes are 3/4 inch or 1 inch. Larger aggregate can be more economical but might not be suitable for thin sections or areas with dense rebar.
- Admixtures: Any specific additives needed (e.g., air-entrainment for freeze-thaw resistance).
- Slump: Your desired workability (e.g., 4-inch slump).
- Color (Optional): If you’re adding pigment for colored concrete.
- Pump Required: Do you need a concrete pump to reach the pour location, or will the concrete truck be able to discharge directly into your forms?
- Delivery Date and Time: Be specific. Confirm the date and a narrow window for the delivery.
- Point of Contact: Who will be on-site to accept the delivery and direct the driver.
- Payment Information: Discuss payment terms.
Pricing Considerations: Concrete Pricing
Concrete pricing varies significantly based on several factors:
- Quantity: Larger orders may have a lower per-yard price.
- Mix Design: Higher PSI mixes, special admixtures, or colored concrete will cost more.
- Delivery Location: Distance from the concrete batch plant can influence delivery fees.
- Minimum Order Fees: Many suppliers have a minimum order quantity, and if you order less, you might be charged the minimum.
- Disposal Fees: If there’s leftover concrete that needs to be disposed of by the supplier.
- Standby Time: If the concrete truck has to wait too long at your site, you’ll likely be charged an hourly fee for standby time. This is why having your site ready is crucial.
It’s a good practice to get quotes from a few different suppliers.
Preparing Your Site for Concrete Delivery
A smooth delivery and pour depend heavily on site preparation.
Forms and Reinforcement
- Forms: Ensure your forms are built sturdy, well-braced, and have the correct dimensions. They should be able to withstand the pressure of the wet concrete.
- Reinforcement: If your project requires rebar or wire mesh, it should be in place and supported at the correct height (often with chairs or dobies) before the concrete arrives.
Access for the Concrete Truck
- Clear Pathways: Ensure a clear, unobstructed path for the concrete truck to reach your pour location. These trucks are large and require ample space.
- Stable Ground: The ground where the truck will be positioned must be firm and level. Soft ground can lead to the truck getting stuck or damaging property. Consider placing plywood or thick boards under the truck’s outriggers for stability.
- Water Source: Have a water source available if minor adjustments to the mix are needed (though this should be done sparingly and ideally in consultation with the driver or supplier).
Tools and Labor Ready
- Tools: Have all necessary tools for spreading, leveling, and finishing the concrete ready and easily accessible: shovels, rakes, screeds, floats, trowels, edgers, and groovers.
- Labor: Ensure you have enough people to help spread, level, and finish the concrete as soon as it arrives. Concrete starts to set quickly, and you need to work efficiently.
The Delivery and Pour: Working with the Concrete Truck
The arrival of the concrete truck marks the beginning of the critical pour phase.
Communicating with the Driver
- Confirm Details: As soon as the truck arrives, confirm the order details with the driver (mix design, quantity).
- Directing the Pour: Clearly direct the driver on where to discharge the concrete. If you’re using a chute, make sure it’s positioned correctly over the forms.
Managing the Pour
- Start Promptly: Begin spreading and leveling the concrete immediately as it’s discharged.
- Avoid Over-Watering: Resist the urge to add too much water to make the concrete easier to work with. This can significantly weaken the final product. If the mix is too stiff, consult the driver.
- Consolidation: Ensure the concrete is properly consolidated to eliminate air pockets. This can be done with a vibrator or by tamping and vibrating the forms.
- Even Distribution: Try to distribute the concrete evenly across the pour area to avoid build-up in one spot while another is still short.
What if You Order Too Little?
If you realize you’ve miscalculated and are running out, call your supplier immediately. They might be able to send another truck, but this will incur additional charges, and a cold joint will form where the new concrete meets the old, creating a weak point. This is why the 10% overage is so vital.
What if You Order Too Much?
If you ordered too much concrete, the supplier might take back a certain amount (usually a quarter or half cubic yard of concrete) if it’s still in good condition and hasn’t been significantly altered on-site. However, there’s often a fee for this. Alternatively, you can use the excess for other small projects like setting posts or creating a small pad. Be sure to clarify the supplier’s policy on returns when you order.
Common Mistakes to Avoid
- Inaccurate Measurements: Not measuring carefully or converting units correctly is the most common error.
- Not Adding Overages: Forgetting the 10% buffer for unexpected needs.
- Underestimating the Slump: Ordering concrete that is too stiff for the application can make finishing difficult.
- Over-Wetting on Site: Adding too much water to make the concrete easier to work with is detrimental to strength.
- Poor Site Preparation: Not having forms ready, reinforcement in place, or clear access for the truck.
- Insufficient Labor: Not having enough people to properly spread, level, and finish the concrete in time.
- Not Considering Weather: Pouring concrete in extreme heat or freezing temperatures without proper precautions can lead to poor results.
Frequently Asked Questions (FAQs)
Q1: How much does concrete cost per yard?
A1: Concrete pricing varies widely. As of late 2023/early 2024, you can expect to pay anywhere from $125 to $200+ per cubic yard of concrete for standard mixes. This price can increase significantly for specialized mixes, admixtures, or if you are below the supplier’s minimum order quantity. Always get a quote for your specific needs and location.
Q2: Can I order less than a cubic yard of concrete?
A2: Most suppliers have a minimum order quantity, often 1 to 3 cubic yards. If you need less than their minimum, you’ll likely be charged the minimum order fee. Some suppliers might offer smaller quantities for a premium, or you may need to look for companies specializing in small-batch concrete.
Q3: What is the difference between ordering concrete and mixing it yourself?
A3: Ordering from a concrete batch plant (ready-mix concrete) ensures a consistent, high-quality mix produced under controlled conditions with precise concrete mix ratio control. Mixing concrete yourself, especially in large quantities, can lead to inconsistent strength and quality due to variations in measurements, mixing time, and water content. For most projects beyond very small repairs, ready-mix is the superior and often more practical choice.
Q4: What is the minimum amount of concrete I can order?
A4: This varies by supplier, but a common minimum order is between 1 and 3 cubic yards. Always confirm the minimum order with your chosen supplier when you call to place your order.
Q5: How long does it take for concrete to set?
A5: Fresh concrete begins to stiffen within about an hour, depending on the mix design, temperature, and humidity. It typically becomes hard enough to walk on in about 24-48 hours. However, concrete continues to cure and gain strength for weeks, and full design strength is usually achieved after 28 days.
Q6: What is a “cold joint” in concrete?
A6: A cold joint occurs when concrete is poured in stages, and the second pour is made after the first has already begun to harden significantly. This creates a weak plane between the two sections, which can be susceptible to cracking and separation. Proper planning to avoid cold joints or using a concrete pump to keep pours continuous is essential.
By carefully calculating your needs, understanding concrete basics, and communicating clearly with your supplier, you can ensure a successful and stress-free concrete ordering and pouring experience.