How Many 90 Lb Bags Of Concrete In A Yard? Solved

To determine how many 90 lb bags of concrete are needed for one cubic yard, you’ll generally need approximately 5 to 6 bags.

Figuring out how much concrete you need for a project can seem tricky. You might be planning a new patio, a small foundation, or perhaps some garden edging. One of the most common questions is: how many 90 lb bags of concrete are in a cubic yard? This is a vital piece of information to ensure you buy enough material without overspending.

Fathoming Concrete Needs: The Cubic Yard Explained

A cubic yard is a unit of volume. Think of it as a cube that is 3 feet long, 3 feet wide, and 3 feet tall. That’s 27 cubic feet of space. When you’re working with concrete, this is the standard measurement for how much you need.

The Math Behind the Bags: Connecting Weight to Volume

Concrete comes in bags of various weights, with 80 lb and 90 lb bags being very common for DIY projects. The key to solving our question lies in understanding the relationship between the weight of a bag and the volume of concrete it yields.

Key Factors:

Bag Weight: We’re focusing on 90 lb bags.
Concrete Density: Dry concrete mix is denser than mixed concrete. When you add water, the volume increases.
Yield: This refers to the actual volume of mixed concrete you get from a bag of dry mix. Manufacturers provide this information, and it’s crucial.

Most 90 lb bags of concrete mix yield approximately 0.75 cubic feet of mixed concrete. This means that for every 90 lb bag you mix with water according to the manufacturer’s instructions, you get about three-quarters of a cubic foot of usable concrete.

Calculating Concrete Per Cubic Yard

Now, let’s put it all together. We know:

1 cubic yard = 27 cubic feet
1 bag (90 lb) ≈ 0.75 cubic feet

To find out how many 90 lb bags of concrete are in a yard, we divide the total volume needed (27 cubic feet) by the yield of one bag (0.75 cubic feet):

27 cubic feet / 0.75 cubic feet/bag = 36 bags

So, theoretically, you would need 36 bags of 90 lb concrete mix to create exactly one cubic yard.

Real-World Considerations: More Than Just Math

While the calculation above gives us a good starting point, real-world projects often require a bit more planning.

Contingency for Spills and Waste

It’s always wise to have a little extra concrete. You might have some spillage during mixing, or the depth of your pour might be slightly more than anticipated in certain areas. A general rule of thumb is to add about 5-10% extra to your total.

For our 36 bags, adding 10% would mean:

36 bags * 1.10 = 39.6 bags

This means you’d likely want to round up to 40 bags of 90 lb concrete to be safe.

Different Bag Sizes: How Many 80 lb Bags of Concrete?

What if you find 80 lb bags are more readily available or cheaper? The calculation is similar. An 80 lb bag typically yields about 0.60 cubic feet of mixed concrete.

27 cubic feet / 0.60 cubic feet/bag = 45 bags

So, you would need approximately 45 bags of 80 lb concrete mix for one cubic yard, plus that contingency.

Using a Concrete Bag Calculator

To simplify these calculations, many resources offer a concrete bag calculator. These online tools are incredibly helpful. You input the dimensions of your project (length, width, and depth) and the type of bag you plan to use (e.g., 90 lb bag), and the calculator does the math for you, often including that important contingency factor. It can quickly tell you how many bags of concrete you need for a patio or any other project.

How Much Concrete Mix Per Yard?

To reiterate, for a cubic yard of concrete, you’re looking at:

90 lb bags: Approximately 36 bags (without contingency).
80 lb bags: Approximately 45 bags (without contingency).

Always check the specific yield information on the concrete bag itself, as this can vary slightly between brands and product types.

Concrete Per Cubic Yard: A Deeper Dive

When professionals talk about concrete per cubic yard, they’re referring to the finished, mixed product. A cubic yard of concrete has a weight of about 4,000 pounds (2 tons). This helps to further contextualize the volume you’re working with.

Bags of Concrete for Patio Projects

Let’s say you’re building a patio that is 10 feet by 12 feet and 4 inches thick.

Step 1: Convert all measurements to feet.

Length = 12 feet
Width = 10 feet
Depth = 4 inches = 4/12 feet = 0.333 feet

Step 2: Calculate the volume in cubic feet.

Volume (cubic feet) = Length × Width × Depth
Volume = 12 ft × 10 ft × 0.333 ft
Volume = 39.96 cubic feet

Step 3: Convert cubic feet to cubic yards.

Volume (cubic yards) = Volume (cubic feet) / 27 cubic feet/yard
Volume = 39.96 cubic feet / 27 cubic feet/yard
Volume ≈ 1.48 cubic yards

Step 4: Calculate the number of 90 lb bags.

Using our previous figure: 1 cubic yard needs about 36 bags of 90 lb concrete.

Number of bags = Volume in cubic yards × Bags per cubic yard
Number of bags = 1.48 cubic yards × 36 bags/cubic yard
Number of bags ≈ 53.28 bags

Step 5: Add contingency.

Let’s add 10% for safety:

53.28 bags × 1.10 ≈ 58.6 bags

So, for this patio project, you would need to purchase approximately 59 bags of 90 lb concrete.

Factors Influencing Concrete Yield

While the general figures are helpful, several factors can influence the actual yield of a concrete bag:

Water Content: Adding too much water will increase the volume slightly but significantly weakens the concrete. Always follow the manufacturer’s recommended water-to-mix ratio.
Compaction: As concrete cures, air pockets can be reduced, leading to a slightly denser final product. However, for typical DIY calculations, this effect is minimal.
Aggregate Size: The size and type of aggregate (gravel and sand) in the mix can subtly affect the overall density and yield.
Bag Quality: Some bags may have slight variations in their fill weight.

Deciphering Bag Coverage: 90 lb Bag Concrete Coverage

The term “coverage” can sometimes refer to how much area a bag will cover at a certain depth, rather than its volume yield. For instance, a 90 lb bag might cover X square feet at a 2-inch depth. This is essentially another way of expressing the volume yield.

If a 90 lb bag yields 0.75 cubic feet, and you’re pouring at a depth of 2 inches (which is 2/12 = 0.167 feet), the area coverage would be:

Area (sq ft) = Volume (cubic ft) / Depth (ft)
Area = 0.75 cubic ft / 0.167 ft
Area ≈ 4.5 sq ft

So, one 90 lb bag will cover approximately 4.5 square feet at a 2-inch depth. This is a useful way to think about it for thin layers like topping or small repairs.

How Many Bags of Cement in a Yard?

It’s important to distinguish between “concrete mix” and “cement.” Cement is just one component of concrete (the binder), along with aggregate (sand and gravel) and water. When you buy a bag labeled “concrete mix” or “concrete,” it already contains cement, sand, and gravel.

If the question is about how many bags of cement are in a cubic yard of concrete, that’s a different calculation and depends heavily on the concrete “recipe” or mix design. A typical concrete mix design might use around 6 to 7 bags of cement (usually 94 lb bags of Portland cement) per cubic yard, along with significant amounts of sand and gravel. However, for DIY projects, you buy pre-mixed bags of concrete, so you don’t need to worry about sourcing individual components.

A Practical Example: Building a Small Footing

Imagine you need to pour a small footing for a fence post. Let’s say the footing needs to be 1 foot long, 1 foot wide, and 8 inches deep.

Step 1: Convert to feet.

Length = 1 ft
Width = 1 ft
Depth = 8 inches = 8/12 ft = 0.667 ft

Step 2: Calculate volume in cubic feet.

Volume = 1 ft × 1 ft × 0.667 ft = 0.667 cubic feet

Step 3: Calculate the number of 90 lb bags.

Number of bags = Volume (cubic ft) / Yield per bag (cubic ft)
Number of bags = 0.667 cubic ft / 0.75 cubic ft/bag
Number of bags ≈ 0.89 bags

Step 4: Add contingency and round up.

0.89 bags × 1.10 ≈ 0.979 bags

You’d definitely need to buy at least 2 bags of 90 lb concrete for this small project. It’s rare for projects to require less than a full bag, so always round up.

The Role of a Concrete Volume Calculator

A concrete volume calculator is your best friend for these types of projects. You input the dimensions, and it outputs the volume in cubic yards. Then, you can use that cubic yard figure to determine how many bags of your chosen weight (like 90 lb or 80 lb) you’ll need. Many also provide an estimate of how many bags of concrete for patio projects or other specific applications.

Frequently Asked Questions

Q: How much water do I add to a 90 lb bag of concrete?
A: Always refer to the instructions on the specific bag you are using. Typically, it’s around 2.5 to 3 quarts of water per 80 lb bag and slightly more for a 90 lb bag, but this can vary by brand and type of concrete mix.

Q: Can I mix concrete in a wheelbarrow?
A: Yes, for small to medium projects, a wheelbarrow is suitable for mixing. For larger volumes, consider a cement mixer.

Q: What is the best way to mix concrete?
A: Add the dry mix to your wheelbarrow or mixer. Gradually add water while mixing thoroughly. The goal is a consistent, workable consistency, not too wet and not too dry. It should hold its shape when squeezed but not crumble apart.

Q: How do I calculate the concrete needed for a specific thickness?
A: Ensure all your dimensions are in the same unit (preferably feet). Multiply length by width by depth (in feet) to get cubic feet. Then, divide by 27 to convert to cubic yards.

Q: What happens if I use too much water in my concrete mix?
A: Using too much water reduces the strength of the cured concrete, making it more brittle and prone to cracking. It also increases the risk of “segregation,” where the heavier aggregates settle to the bottom.

Q: How can I ensure my concrete is the correct depth?
A: Use screed boards or forms to guide your leveling process. Measuring the depth regularly as you pour and finish will help you achieve consistent thickness.

By carefully calculating your needs and using resources like a concrete bag calculator or understanding how to determine concrete per cubic yard, you can confidently tackle your next DIY project. Remember, it’s always better to have a little extra concrete than to run short!