Bags of Cement in a Cubic Yard? Exact Count

You need about 45 bags of 80-pound cement to make 1 cubic yard, or 60 bags of 60-pound, or 90 bags of 40-pound. This assumes you’re using standard pre-mixed concrete mix (which contains cement, sand, and gravel), not pure Portland cement. The exact count depends on bag weight and how thick you pour the slab.

Formula

The volume of a rectangular slab is length × width × depth. To convert cubic feet to cubic yards, divide by 27 (since 1 yard = 3 feet, and 3³ = 27). If your depth is in inches, first convert to feet by dividing by 12.

Volume (yd³) = (Length (ft) × Width (ft) × Depth (in) ÷ 12) ÷ 27

Simplified: Volume (yd³) = Length × Width × Depth ÷ 324

Where:

• Length and Width are in feet
• Depth is in inches
• 324 = 12 inches per foot × 27 cubic feet per cubic yard

Worked Example

Using the defaults from the calculator above (40 ft × 25 ft × 3 in):

1. Convert depth to feet: 3 in ÷ 12 = 0.25 ft
2. Volume in cubic feet: 40 × 25 × 0.25 = 250 ft³
3. Convert to cubic yards: 250 ÷ 27 = 9.26 yd³

The calculator shows 9.26 yd³, matching the formula exactly.

Why Bag Count Varies

Pre-mixed concrete bags are sold by weight, and the weight determines how much finished concrete you get. An 80-pound bag yields about 0.6 cubic feet of wet concrete. A 60-pound bag yields about 0.45 cubic feet. A 40-pound bag yields about 0.30 cubic feet.

Since 1 cubic yard equals 27 cubic feet, divide 27 by the yield per bag:

• 80-lb bag: 27 ÷ 0.6 = 45 bags
• 60-lb bag: 27 ÷ 0.45 = 60 bags
• 40-lb bag: 27 ÷ 0.30 = 90 bags

These yields are standard for pre-mixed concrete (often labeled as “4000 psi mix”). Pure Portland cement, if you were mixing your own with sand and gravel, has a different volume per bag, but for most DIY projects you’re buying pre-mixed.

How to Choose the Right Bag Size

For small projects like setting fence posts or repairing a walkway, 40- or 60-pound bags are easier to lift and mix. For a slab or footing, 80-pound bags reduce the number of batches, but they’re heavy—many people can’t safely lift an 80-pound bag repeatedly.

Consider the number of bags you’ll need overall. If you need more than about 20 bags, it’s often cheaper and easier to order ready-mix concrete delivered by truck. A cubic yard is a typical minimum order for many ready-mix companies.

Common Mistakes

The most frequent error is mixing up cubic feet and cubic yards. A slab that is 10 ft × 10 ft × 4 in is 33.3 cubic feet, which is only 1.23 cubic yards—not 33.3 yards. Always divide by 27.

Another mistake is ignoring the depth in inches. If you measure depth in inches but use feet for length and width, you must divide by 12 first. The formula above (÷ 324) does that automatically.

Also, bag yields are approximate. They assume you mix the concrete with the recommended amount of water and that you don’t lose any to spillage. In practice, add 5-10% extra to your order to account for waste, uneven subgrade, or slight miscalculations.

Cost Comparison: Bags vs. Ready-Mix

Bags are more expensive per cubic yard than ready-mix, but you pay for convenience and no minimum order. For a small project (less than half a yard), bags are the practical choice. For anything larger, ready-mix is usually cheaper and more consistent.

However, bags give you control over mixing and setting time. You can mix only what you need, and you don’t need a truck to access the site. Ready-mix requires a driveway or path for the truck, and you must be ready to place all the concrete quickly before it sets.

Safety and Handling

Concrete mix contains Portland cement, which is caustic. Wear gloves, long sleeves, and eye protection when handling dry mix. Avoid inhaling dust, and wash skin immediately if it contacts wet concrete. Cement burns can be serious.

Lifting 80-pound bags repeatedly can strain your back. Use proper lifting technique (bend knees, keep back straight) or use a wheelbarrow to move bags. For large projects, consider renting a mixer or having a friend help.

Frequently Asked Questions

How many 80-lb bags make a yard of concrete?

Exactly 45 bags. Each 80-lb bag yields about 0.6 cubic feet, and 27 cubic feet (1 yard) divided by 0.6 equals 45.

How many square feet does a cubic yard cover?

It depends on thickness. At 4 inches deep, one cubic yard covers 81 square feet (27 ft³ ÷ 0.333 ft). At 6 inches deep, it covers 54 square feet. Use the calculator above with your dimensions to get a precise number.

Is a cubic yard the same as a ton?

No. A cubic yard is a volume, while a ton is a weight. Concrete weighs about 4,000 pounds per cubic yard (roughly 2 tons), but this varies with the mix and moisture. Bags are sold by weight, so you can’t directly convert without knowing the density.

Can I mix concrete in a wheelbarrow?

Yes, for small batches. A typical wheelbarrow can handle one 60-lb bag at a time. For larger projects, a portable cement mixer is faster and ensures a more consistent mix. Never mix more than you can place within the working time (usually 30-60 minutes).

What happens if I add too much water?

Too much water weakens the concrete and increases shrinkage cracking. The mix should be workable but not soupy. Follow the water ratio on the bag, and add water gradually until the concrete is moldable but not dripping.

Do I need rebar or wire mesh?

For a simple patio or walkway, wire mesh helps control cracking. For structural slabs, footings, or driveways, rebar is typically required. Check local building codes for specific requirements based on your project and soil conditions.

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in l | Lawn length | ft | 40 | 0 | 100000
in w | Lawn width | ft | 25 | 0 | 100000
in d | Depth | in | 3 | 0 | 120
out yd | Volume | yd³ | l * w * d / 324 | 2
out ft3 | Volume | ft³ | l * w * d / 12 | 1