Building a concrete in-ground pool is a significant investment, and one of the most critical components of the project is determining how much concrete you’ll need. Whether you’re laying the foundation for the pool structure or building the surrounding deck, understanding the volume of concrete required—especially for a 20×40 pool—is essential to budgeting, planning, and executing your project successfully.
In this comprehensive guide, we’ll walk you through everything you need to know about calculating the amount of concrete required for a 20×40 pool, including factors that influence the volume, estimating techniques, and helpful tips to ensure your project runs smoothly.
Understanding the Role of Concrete in Pool Construction
Concrete is a key material used in constructing in-ground pools, particularly in the forms of shotcrete (gunite) or poured concrete. It serves as the structural base for the pool walls, floor, and surrounding structures such as decks and retaining walls.
Types of Concrete Used in Pool Building
There are two primary types of concrete used in pool construction:
- Shotcrete (Gunite): A dry-mix concrete that’s pneumatically projected onto the pool form. It’s known for its high strength and flexibility.
- Poured Concrete: Traditional wet-mix concrete that’s poured into molds. It’s less commonly used due to the complexity of formwork needed.
Both methods can be effective, but shotcrete is preferred for its adaptability and strength in shaping complex pool geometries.
Factors That Affect Concrete Usage for a 20×40 Pool
Before you can begin calculating, you need to understand the variables that influence how much concrete you’ll need. These include:
1. Pool Depth and Shape
A 20×40 pool may be rectangular, L-shaped, curved, or have varying depths. A shallow, flat-bottomed pool will use less concrete than a deep-end construction with slopes or stairs.
2. Structural Components
Concrete is used for multiple parts of the pool system, including:
- The floor and walls of the pool
- Pool deck (if included)
- Coping and tiling bases
- Stands, steps, and patios
Each of these contributes to the total amount needed.
3. Soil Conditions and Local Requirements
Clay or loose soils may require additional footing and reinforcement. Local building codes also dictate minimum thicknesses for structural elements like walls and floors.
4. Finish Type
Different finishes require different preparatory coats. For example, a plaster finish typically requires a smooth shotcrete base, while tile finishes need additional concrete backing for tiles and coping.
5. Add-Ons and Custom Features
If your design includes benches, sun shelves, or tanning ledges, these will each add to the amount of concrete needed.
Calculating the Concrete Needed for a 20×40 Pool
Let’s break it down step by step.
Step 1: Determine the Pool Dimensions
For this article, we’ll use a standard rectangular 20×40 pool as the base model. For simplicity, assume an average depth of 5 feet with a shallow end of 3 feet and a deep end of 7 feet.
Step 2: Calculate the Volume of Concrete
For a Gunite or Shotcrete Pool Shell
A typical 20×40 pool requires between 50 and 70 cubic yards of concrete for the shell alone. Here’s why the range exists:
- Average thickness: Pool walls are typically 8 to 14 inches thick, while the floor is 6 to 10 inches.
- Design features: Sloped bottoms, steps, and raised ledges add volume.
- Reinforcement: Rebar grids or welded wire fabric can create pockets requiring more material.
A general formula to estimate the concrete for the shell is:
- For walls: Calculate total square footage of walls (height * perimeter) and multiply by 0.5–0.75 inches of thickness converted to feet (usually 0.05 to 0.07 feet).
- For floor: Area of floor (length * width) multiplied by thickness of floor (6–10 inches = 0.5–0.8 feet).
Adding these two together gives cubic feet, which you then convert to cubic yards (1 cubic yard = 27 cubic feet).
For the Decking Around the Pool
If your project includes a concrete pool deck, an additional 10–20 cubic yards may be needed, depending on:
- Deck size (usually 4–6 feet wider on all sides)
- Concrete slab thickness (4–6 inches standard)
- Design elements like stamped concrete or integrated pavers
A 20×40 pool with a 20-foot by 60-foot deck area (including the pool) at 4 inches thick would need about 14.8 cubic yards of concrete or roughly 15 cubic yards.
Step 3: Include Additional Structural Elements
Some projects may require:
- Concrete steps, benches, or sun decks inside the pool
- Vaults, beam reinforcements, or footers
- Foundation walls for pool equipment (pump house, cabana)
These custom components typically require 3–10 yards more of concrete.
A Concrete Volume Estimate Table
| Component | Approximate Volume (Cubic Yards) | Notes |
|---|---|---|
| Pool Shell | 50–70 | Shotcrete application |
| Pool Deck (10-ft perimeter) | 10–20 | 4–6 inches thick |
| Structural Add-Ons (beams, steps, etc.) | 3–10 | Custom features |
| Total Estimated Concrete | 65–100 | Varies with depth, soil, and design |
How to Minimize Concrete Waste and Cost Overruns
Concrete is expensive, and proper planning is key to avoiding unnecessary expenses. Here are strategies to help you manage your concrete budget effectively.
1. Work with a Skilled Pool Contractor
Experienced contractors can provide accurate estimations and help tailor your design to minimize material waste.
2. Review Local Building Codes
Structural requirements vary by region. Knowing what’s mandatory ensures you order the correct amount without overbuilding.
3. Use Rebar and Mesh Effectively
Proper reinforcement allows you to use slightly thinner concrete in some areas, optimizing material use.
4. Calculate for Slopes and Voids
When you have deeper ends or sloped walls, the shotcrete team may use less concrete in certain areas due to slope dynamics.
5. Consider Pre-Fabricated Accessories
Installing prefabricated steps or benches that are designed to fit within existing structural walls can decrease the amount of custom concrete needed.
Other Materials Needed for Pool Construction
Concrete is just one part of the building process. You’ll also need:
- Rebar: To reinforce structural integrity.
- Plumbing pipes: For filtration system layout.
- Pool shell finish: Plaster, epoxy, pebble, or tile.
- Formwork and bracing (if poured concrete is used)
- Grading and excavation tools: For preparing the site before concrete work begins.
While these don’t directly affect your concrete volume, their availability impacts the efficiency and timing of your concrete work.
When to Order Concrete and How to Prepare
Concrete delivery is a logistical challenge involving timing, space, and equipment. Here’s how to get ready.
1. Finalize the Design Plan
Ensure all features and dimensions are locked in before placing the order to avoid last-minute adjustments.
2. Create Access for Concrete Trucks
A 20×40 pool area must have enough clearance for trucks to maneuver. A minimum width of 12 feet is recommended for delivery.
3. Schedule Delivery and Application Times
Shotcrete applications often take 1–2 days. Coordinate delivery schedules with the timeline of rebar installation and form preparation.
4. Store Backup Materials
If using gunite, which mixes water at the nozzle, ensure backup supplies of dry mix and aggregates are accessible on-site.
5. Weather Considerations
Avoid ordering during rainy or extremely hot weather unless your contractors are prepared to handle these conditions.
What to Expect During Concrete Application
The method of application depends on whether you’re using shotcrete or poured concrete.
Gunite/Shotcrete Process
- Digging and grading the excavation pit
- Bending and tying the rebar cage for the pool structure
- Setting up formwork or guides for walls and floor
- Blowing gunite in layers to desired thickness
- Hand troweling and shaping for plumbing and niche openings
- Allowing time for curing (28 days for full set)
Poured Concrete Method (Less Common)
This involves more labor to build forms, insert rebar, and pour concrete in sections. It’s preferred for modular or precast designs.
The Cost of Concrete for a 20×40 Pool
Concrete costs vary by location, volume ordered, and labor involved. Here’s a general breakdown:
Gunite/Shotcrete Costs
- Material: $50–$60 per cubic yard
- Labor and application: $7–$12 per square foot
For a 3,000-square-foot pool area (20×40 = 800 sq ft + deck area), the combined cost could range from $40,000 to $60,000+ for concrete alone.
Deck Concrete Costs
- Material: ~$100–$120 per cubic yard (higher due to finish additives)
- Finishing labor: $4–$8 per square foot
Total deck material cost for 15 cubic yards might run $1,800–$2,500, with an additional $3,000–$5,000 for finish work.
Final Tips for Ensuring Accuracy and Cost-Effectiveness
Here are the top recommendations from professional pool builders:
- Double-check all dimensions before ordering.
- Factor in a 5–10% extra margin for waste or adjustments.
- Use professional volume calculation tools or apps (like Pool Volume Calculator or Concrete Estimator Tools).
- Compare quotes from multiple concrete suppliers and contractors.
Conclusion: Planning Your Concrete Needs Pays Off
Understanding how much concrete you need for a 20×40 pool is essential to keeping your project on time and on budget. Whether you’re preparing for the gunite shell, a surrounding deck, or custom features like seating and ledges, clear calculations and proactive communication with your contractor will ensure the best results.
By factoring in depth, design preferences, structural requirements, and local codes, you’ll have the knowledge and confidence to guide your project through the concrete phase seamlessly. Remember, accurate estimation is a blend of science and experience—working with a seasoned professional is your best investment.
How do I calculate the amount of concrete needed for a 20×40 pool?
To calculate the amount of concrete needed for a 20×40 pool, start by determining the dimensions and thickness of the concrete slab. A typical pool pad requires a minimum of 4 inches of concrete, but in colder climates or for heavier pools, a thickness of 6 inches may be necessary. Multiply the length (20 feet) by the width (40 feet) to get the total surface area, then multiply by the thickness (converted to feet) to find the cubic footage of concrete required.
Once you have the cubic footage, divide by 27 to convert it to cubic yards, which is the standard unit used by concrete suppliers. For example, a 4-inch thick slab (0.33 feet) for a 20×40 pool would cover an area of 800 square feet, resulting in approximately 264 cubic feet. Dividing that by 27 gives around 9.78 cubic yards of concrete. It’s always wise to add an extra 5–10% to account for spillage or inconsistencies in the pour. This ensures you’ll have enough concrete without running short during the project.
What type of concrete should I use for a swimming pool foundation?
For a swimming pool foundation, it’s essential to use high-strength concrete that can support the weight of the pool and water. A minimum compressive strength of 3,500 psi is recommended for residential applications, but many contractors opt for 4,000 psi concrete or more, especially in areas with freeze-thaw cycles. Using air-entrained concrete can also improve durability by allowing the material to withstand weather-related stress.
The concrete mix typically includes cement, sand, gravel or crushed stone, and water in the right proportions to achieve both strength and workability. Reinforcing the slab with rebar or wire mesh is also standard practice, which helps prevent cracking and provides added structural integrity. Choosing a licensed concrete supplier and consulting with a professional contractor ensures that the concrete used is appropriate for your specific pool design and environmental conditions.
Can I pour the concrete slab for a 20×40 pool myself?
It is possible to pour a concrete slab for a 20×40 pool yourself, but it requires careful planning, physical labor, and some knowledge of concrete work. The process involves site preparation, formwork, rebar installation, and timely pouring and finishing. If you are inexperienced, even a small mistake can lead to cracking, uneven settling, or other structural issues, making it important to understand all the steps involved.
Hiring a professional contractor is often a safer option, particularly because they have the equipment and expertise to handle large volumes of concrete efficiently. They will also ensure that the ground is properly compacted, that drainage is sufficient, and that the slab is level and correctly reinforced. However, if you decide to tackle the project yourself, it’s wise to consult with professionals or watch instructional videos to understand best practices and avoid common pitfalls.
How long does it take for the concrete to cure before I can install the pool?
A concrete slab for a 20×40 pool must cure sufficiently before the pool can be installed. Under average conditions, concrete reaches about 70% of its strength within 7 days, and full strength (around 100%) after 28 days. During this time, it’s important to keep the surface moist and covered to ensure proper curing, especially in hot or dry climates.
Premature loading or exposure to moisture variations can compromise the integrity of the slab. If the pool is installed too early, the weight of the water and structure may cause cracks or uneven settling. Always check with your contractor or the pool manufacturer for their recommended curing time before proceeding. Curing compounds or coverings like plastic sheeting and wet burlap can be used to maintain optimal moisture during the critical first week and beyond.
Do I need permits or inspections for pouring concrete for a pool?
Yes, in most areas, you’ll need building permits and inspections for pouring concrete for a pool, particularly if it’s a permanent, in-ground installation. Permits ensure that the work adheres to local zoning laws, building codes, and safety regulations. The inspection process often includes checks on the excavation, reinforcement, formwork, and the final poured slab.
The requirements vary depending on your location, so it’s best to contact your local municipal building department before beginning any work. They can outline the necessary forms, fees, and specific construction guidelines. Failure to obtain permits can lead to legal issues, fines, or complications when selling your property. Working with a licensed contractor can help streamline this process, as they will often handle permits and inspections on your behalf.
What kind of preparation is needed before pouring the concrete slab?
Before pouring the concrete slab for a 20×40 pool, thorough site preparation is crucial. The first step is excavating the area to the appropriate depth, which typically includes space for a gravel base, rebar, and the concrete itself. The ground should be compacted to prevent shifting and settling, and a vapor barrier (like plastic sheeting) is often added to control moisture migration.
Additionally, it’s important to install proper drainage solutions around the pool pad to avoid water accumulation under the slab. Steel rebar or mesh is placed systematically across the slab area to support the concrete and reduce cracking. Forms are also built and secured around the perimeter to contain the concrete during the pour. Accurate layout and leveling at this stage are essential to ensure a strong, durable foundation for the pool.
How much does it cost to pour a concrete slab for a 20×40 pool?
The cost to pour a concrete slab for a 20×40 pool varies depending on several factors such as location, concrete quality, labor rates, and site preparation requirements. On average, concrete costs between $5.00 to $10.00 per square foot for a basic slab. For a 20×40 pool pad (800 square feet), this translates to a range of approximately $4,000 to $8,000 for materials and labor combined.
Additional costs may arise from grading, excavation, drainage improvements, rebar reinforcement, and any required permits or inspections. If the site has soft or unstable soil requiring extensive work, or if special concrete mixes are used, expenses can increase further. To manage the budget effectively, obtain multiple quotes from licensed contractors and suppliers, and get a clear understanding of what each quote includes before proceeding.