How Much Does a 20×40 Concrete Slab Cost in 2024?

Concrete slabs are versatile structures and have many uses. You can use them as flooring for your barndominium, a walkway, or a roof if you plan on having a roof deck. If you plan on building a small barn or a small barndominium for guests or in-laws, a 20×40 concrete slab is an excellent flooring option. 

Before you fork out money for a concrete slab, you must know how much you need to spend and the items you will spend your money on. Making a concrete slab involves several expenses, including buying materials, hiring a contractor, or renting equipment, and we will discuss all these items to know what you are getting into. 

This article gives you an in-depth look at concrete slabs, their components, and how to know how much you are expected to spend while making a 20×40 concrete slab. 

What Factors Determine the Cost of a 20×40 Concrete Slab?

Determining the cost of a concrete slab hinges on several factors. The most obvious factor is the size of the concrete slab you intend to make. A 20×40 concrete slab will result in an area measuring 800 square feet, so you’ll need a considerable amount of building materials. 

You also need to consider the cost of the building materials you will use. This depends on your location because the cost of materials can vary depending on where you live. If you have a local supplier you frequently order from, you might get lucky and receive discounts.

If you don’t know a supplier, approach several suppliers and ask for their quotes. This will allow you to compare prices so that you can order from the supplier offering the most reasonable price. 

How Much Does a 20×40 Concrete Slab Cost?

The cost of a 20×40 concrete slab will also depend on the characteristics of the slab you are making. Let’s check how each characteristic affects the pricing of a slab.  

Per Thickness

If you are new to making a concrete slab, it might surprise you to learn that they come in several thickness levels. The thickness of a concrete slab is critical because it will determine where you can use a slab. For example, a thin slab is cheaper because it will use fewer materials, but you cannot use it on a load-bearing structure because it will crack.

An example we mentioned earlier is if you intend to build a concrete slab roof because you want a roof deck. A roof deck will need a thick concrete slab to support the weight, not just of the equipment you will put on it but also of the people you plan on entertaining on your roof deck. You will also need thick concrete slabs for the flooring of barndominiums, pole barn homes, and shouses. 

Thickness	Cost per square foot
4 inches	$5.35
5 inches	$5.80
6 inches	$6.20
8 inches	$7

Inclusions

Concrete slabs have inclusions or the items you need in making one. These are items that a concrete slab cannot do without, so you cannot skip them. A reinforcing bar or rebar is an example of inclusion. Why is it important? For one, a rebar can help provide a form to your concrete slab. A rebar is also crucial because it improves the tensile strength of a concrete slab.

With the help of a rebar, an 800 square feet concrete slab will be more durable and able to resist cracks. A wire mesh is an excellent alternative to rebars. It is a steel fabric material you can use to make square grid patterns on your concrete form. Like a rebar, a wire mesh can strengthen a concrete slab. However, a mesh wire is not as bulky and heavy as a rebar. 

Inclusion	Cost
Cement Mixer	Prices start at $439 (2)
Concrete Mixer Rental	$97 per day (3)
Concrete Rebar	$1.40 – $1.85 per 2 feet (4)
Wire Mesh	$0.28 per square foot (5)

With Additional Features

Some concrete slabs have additional features depending on how you want to use them. For example, if your floor plan includes a basement, you will need to install a vapor barrier on the basement’s concrete slab floor. A vapor barrier is a material that prevents moisture from entering a concrete slab.

Since basements are prone to moisture and leaks, a vapor barrier gives your basement an additional layer of protection. This can minimize or prevent the growth of mold that might cause health issues to a building’s occupants. Adding a vapor barrier can increase your barndominium cost but will eventually safeguard your investment. 

Features	Cost
Vapor barrier	$0.50-$0.70 per square foot (6)
Stamped concrete	$9 – $20 per square foot, inclusive of materials (7)
Stained concrete	$2 – $4 per square foot, staining only (8)

20×40 Concrete Slab Cost Breakdown

Let’s take a quick look at the different components of a concrete slab and the cost of each one. 

Concrete Bag Cost Estimate

If you want to make a concrete slab, you’ll need to buy bags of concrete mix since this is the chief component of concrete slabs. The average cost of a concrete mix bag is between $4.50 and $27 each ⁽⁹⁾. You have a pretty wide range because the bag’s size and the mixture’s type affect pricing.  

Labor Cost Estimate

You need to account for labor costs if you are hiring professionals to make your 800-square-foot concrete slab. Expect to pay between $2-3 per square foot, but the rates may be higher if you hire a contractor with excellent credentials ⁽¹⁰⁾. 

Truck Cost Estimate

Properly mixing concrete is vital in making a slab because it can affect your slab’s durability. Alternatively, Instead of mixing concrete by yourself, you can have wet concrete delivered. Concrete delivery costs between $125 and $133 per cubic yard ⁽¹¹⁾. However, if your site is outside the supplier’s service area, the supplier might charge fuel surcharges ranging between $20 and $40 per truckload ⁽⁹⁾. 

How Do You Calculate the Cost of a 20×40 Concrete Slab?

We’ve discussed the various components of a concrete slab, so let’s get down to computing how much a 20×40 concrete slab costs. We will provide you with several price cost averages and sample computations you can use as guides. 

The first thing we need to do is determine how much concrete your 800-square-foot concrete slab will need. We are using six inches as the reference thickness since this is the average thickness of most concrete slabs. This calculator shows that a 6-inch thick concrete slab measuring 800 square feet will use 14.815 cubic yards of concrete.

We will add another 10% as a wastage allowance, so you’ll need 16.3 cubic yard of concrete mix. Based on data from the National Ready Mixed Concrete Association ⁽¹²⁾, the average cost of ready-mixed concrete in 2022 is $137 per cubic yard, so you’ll spend around $2,233.1 for 16.3 cubic yards of concrete mix. 

Let us now compute how much 800 sq. ft. of concrete will cost. A square foot of 6-inch thick concrete slab costs $6.20 ⁽¹⁾. When we multiply 800 by 6.2 and add the 10% wastage allowance, the total will be $5,456.  

Should You DIY or Hire a Contractor for Your 20×40 Concrete Slab Project?

Making a 20×40 concrete slab yourself can help you save money, but we recommend hiring a professional. Although a contractor entails additional costs, hiring one can ensure that the concrete slab gets done quickly and correctly. Remember that the concrete slab is integral to your structure’s integrity, so you don’t want to take risks. 

Conclusion

Knowing how to compute the costs of construction projects is important in preparing a proper budget, and concrete slabs are no exemption. Using the formula discussed earlier; you can determine how much a 20×40 concrete slab will cost to know if your contractor is being truthful or overcharging you. Follow our Facebook page to learn about other important topics like barndominium financing, DIY tips, and design ideas. 

References

1. How Much Does A Concrete Slab Cost In 2023? Homeadvisor.
2. Cost Of A Concrete Driveway ConcreteNetwork
3. What Are Common Rebar Prices for Concrete Projects? Angi
4. How to Compare the In-Place Cost of Wire Mesh Versus Synthetic Fibers ABC Polymer Industries
5. How Much Does Crawl Space Encapsulation Cost? Angi 
6. Stamped Concrete Cost For Patios, Driveways & More ConcreteNetwork
7. Concrete Floor Cost – What You’ll Pay For Polished Or Stained Concrete ConcreteNetwork
8. How Much Does Concrete Cost? Angi
9. How Much Does a New Concrete Slab Cost? Angi
10. How Much Does It Cost to Have Concrete Delivered in Your Area? Fixr
11. Ready Mixed Concrete Industry Data Survey. NRMCA