How Many Bags of Concrete Do I Need?

Figuring out how many bags of concrete you need is a straightforward math problem, but the wrong answer means stopping mid-pour or hauling back 30 bags you didn't use. Local Concrete Contractor is a North Carolina–based concrete company in business 15 years, with hundreds of 5-star Google reviews across Charlotte, Raleigh, the Triad, and the Lake Norman area. Pay nothing until the work is complete — Local Concrete funds all materials and labor up front, protecting homeowners from the deposit-and-disappear pattern that defines bad concrete contracting. This post gives you the exact formula, bag-yield tables, project-specific examples, and a clear decision point for when bagged concrete stops making sense and ready-mix becomes the smarter call.

The concrete bag formula

The calculation has three steps: find cubic feet, divide by bag yield, and add a waste buffer. Here is the formula written out:

1. Cubic feet = Length (ft) × Width (ft) × Depth (ft)
2. Bags needed = Cubic feet ÷ Yield per bag
3. Purchase quantity = Bags needed × 1.10

Depth must be converted from inches to feet before you multiply. Divide inches by 12: 4 inches becomes 0.333 feet, 6 inches becomes 0.5 feet.

Worked example: 12×20 driveway apron at 4 inches

Length 12 ft × Width 20 ft × Depth 0.333 ft = 79.9 cubic feet. Divide by 0.60 (80-pound bag yield) = 133 bags. Multiply by 1.10 = 147 bags. At roughly $6.50 per 80-pound bag at a home center, that is about $955 in material alone — a useful reality check before you decide whether ready-mix makes more sense. For a deeper look at how much a concrete driveway costs including labor and finishing, we cover that separately.

Worked example: 4×8 walkway at 4 inches

4 ft × 8 ft × 0.333 ft = 10.7 cubic feet. Divide by 0.60 = 17.8, round up to 18. Add 10 percent = 20 bags. A small project like this is a clear candidate for bagged concrete mixed by hand or with a rented paddle mixer.

Circular slabs and irregular shapes

For a circular pad, use the formula: π × radius² × depth. A 10-foot-diameter circular patio (radius = 5 ft) at 4 inches thick: 3.14159 × 25 × 0.333 = 26.2 cubic feet. Divide by 0.60 = 43.6, round up to 44, add 10 percent = 49 bags. For L-shapes or irregular yards, break the area into rectangles, calculate each, and add the totals.

Bag yield by size and project type

Bag yield varies by weight. The table below shows how many bags you need per cubic yard (27 cubic feet) for the three most common bag sizes, along with typical project applications.

Bag size	Yield per bag	Bags per cubic yard	Best for
40-pound	0.30 cu ft	90 bags	Post holes, small repairs, steps
60-pound	0.45 cu ft	60 bags	Sidewalks, small patios, fence posts
80-pound	0.60 cu ft	45 bags	Driveways, patios, slabs, foundations

The 80-pound bag is the most cost-efficient per cubic foot for large pours. The 40-pound bag is easier to lift and maneuver solo, making it popular for post holes and repair patches where precision matters more than volume.

Quick reference: common project sizes and bag counts

Project	Dimensions	Thickness	80-lb bags (with 10% buffer)
Small patio	10×10 ft	4 in	~50 bags
Medium patio	12×16 ft	4 in	~98 bags
Sidewalk	3×20 ft	4 in	~37 bags
Single-car driveway	10×20 ft	5 in	~154 bags
Fence post hole (10-in dia × 24-in deep)	Per hole	N/A	~1 bag (80-lb)

If you are planning a full driveway replacement rather than an apron repair, the single-car numbers above are only the starting point. Learn more about choosing the right concrete driveway thickness before finalizing your pour depth.

When to use ready-mix instead

Bagged concrete makes sense up to about 1 cubic yard. Beyond that, a ready-mix delivery truck almost always wins on cost, consistency, and labor.

One cubic yard equals 45 bags of 80-pound mix. At roughly $6.50 per bag, that is approximately $293 in bags alone — before mixing labor, equipment rental, and the physical toll of hand-mixing. A cubic yard of ready-mix concrete delivered in Charlotte or Raleigh typically costs $125 to $180, plus a short-load fee if you order less than a full truck (usually 10 cubic yards). Short-load fees typically run $15 to $25 per cubic yard under the minimum.

Beyond cost, ready-mix offers a controlled mix design: the water-cement ratio, aggregate size, slump, and PSI are dialed in at the plant. According to the National Ready Mixed Concrete Association (NRMCA), ready-mix plants operate under strict quality-control protocols that are difficult to replicate on a job site with bagged material.

Decision checklist: bags vs. ready-mix

• Use bags if the project is under 1 cubic yard, in a tight access area, or a phased repair.
• Use ready-mix if the project is over 1 cubic yard, requires a specific PSI or mix design, or must be poured in a single continuous session to avoid cold joints.
• Always use ready-mix for structural foundations, retaining walls over 4 feet, and pool decks where air entrainment and fly ash content must be specified.

For more guidance on full poured-concrete projects handled by a professional, see our breakdown of concrete patio cost and what affects the final price.

Mix design, PSI, and water-cement ratio

Most standard bagged concrete mixes are designed to achieve 3,000 to 4,000 PSI at 28 days when mixed correctly. PSI requirements vary by application.

• Sidewalks and patios: 3,000 PSI minimum
• Driveways: 3,500 PSI recommended, 4,000 PSI for heavy vehicles
• Structural foundations: 4,000 PSI minimum, often 5,000+ PSI
• Stamped concrete and decorative concrete: 4,000 PSI to resist surface wear

According to the American Concrete Institute (ACI), the single biggest variable in field-mixed concrete quality is the water-cement ratio. Every extra quart of water added to a bag to make mixing easier can reduce compressive strength by 400 to 600 PSI. Always follow the manufacturer's water recommendation, typically 3 quarts per 80-pound bag.

In North Carolina's Piedmont and mountain regions — areas around Winston-Salem, Greensboro, Statesville, and Hickory — freeze-thaw cycles are significant enough to require air-entrained concrete. Air entrainment (typically 5 to 7 percent air by volume) creates microscopic bubbles that give water room to expand as it freezes, dramatically reducing scaling and spalling. If you are purchasing bagged mix for a driveway or exposed slab in those regions, look for bags specifically labeled "air-entrained" or add an air-entraining admixture to a standard mix. According to the Portland Cement Association (PCA), air-entrained concrete exposed to freeze-thaw cycles performs significantly better over a 10-to-20 year service life than non-air-entrained mix at the same PSI.

What about high-early-strength and fast-setting bags?

Fast-setting bagged mixes like Quikrete Fast-Setting or Sakrete Fast-Setting are designed to set in as little as 20 to 40 minutes. They are useful for setting fence posts and mailbox posts, but they are not appropriate for large poured slabs because the rapid set time makes it nearly impossible to screed, finish, and control-joint a full slab before the mix stiffens. Stick with standard 3,000 or 4,000 PSI mix for any project larger than a post hole. See our article on concrete sidewalk cost and materials for how mix selection affects the final price.

Subgrade preparation and reinforcement

The number of bags you pour matters far less than the surface you pour them on. A perfectly calculated bag count poured over a poorly compacted subgrade will crack, settle, and fail within a few years.

Subgrade preparation steps

1. Excavate to the required depth: slab thickness plus 4 inches for a gravel base.
2. Remove all organic material, roots, and loose soil.
3. Compact the native soil with a plate compactor. According to the Federal Highway Administration (FHWA), inadequate subgrade compaction is among the leading causes of premature slab failure in residential concrete work.
4. Add a 4-inch layer of crushed stone or gravel and compact again.
5. Install forms at the correct grade and check for level.

North Carolina's clay-heavy soils — common throughout the Charlotte metro, Raleigh, Cary, and the Triad — are particularly prone to expansion and contraction with moisture changes. This soil movement transfers directly to the slab as settlement cracking and frost heave if the subgrade is not properly prepared. For guidance specific to NC clay conditions, NC State Extension provides resources on soil stabilization and drainage for residential projects.

Rebar, wire mesh, and fiber reinforcement

Reinforcement does not increase the number of bags you need, but it is part of every well-planned pour. Here is when each type applies:

• Wire mesh (6×6 W1.4×W1.4): Standard for residential patios and sidewalks. Position mesh in the middle third of the slab, not flat on the ground. Use wire chairs or broken concrete fragments as spacers.
• Rebar (#3 or #4 bar): Required for driveways, pool decks, and any slab subject to vehicle loads. Space at 18 inches on center in both directions for a 4-inch driveway slab.
• Fiber reinforcement: Polypropylene or steel fibers added at the mixer reduce plastic shrinkage cracking and crazing at the surface. Fiber does not replace structural steel but adds a useful secondary layer of crack control.

For projects that require both structural steel and a decorative surface — such as stamped concrete patios or exposed aggregate driveways — reinforcement planning is critical. Our guide to stamped concrete vs. pavers walks through why slab thickness and reinforcement affect both durability and resale value.

Expansion joints and control joints

Concrete expands and contracts with temperature. Without proper joint placement, the slab will crack where it wants to rather than where you planned. Control joints should be cut or tooled to a depth of one-quarter the slab thickness (1 inch for a 4-inch slab) every 8 to 10 feet. Expansion joints filled with a compressible material should be placed wherever the slab meets a structure, such as a house foundation or existing curb.

Curing: the step most DIYers skip

Curing is the process of keeping fresh concrete moist and at the right temperature so the Portland cement fully hydrates and achieves its rated PSI. Most homeowners stop thinking about their pour once the finishing is done, but curing determines whether that 4,000 PSI bag mix actually reaches 4,000 PSI or falls short at 2,800 PSI.

The ACI recommends moist curing for a minimum of 7 days for standard Portland cement mixes. In practice, that means one of the following:

• Cover the slab with wet burlap or curing blankets and keep them damp for 7 days.
• Apply a liquid curing compound (membrane-forming curing compound per ASTM C309) immediately after finishing.
• Cover with plastic sheeting sealed at the edges to trap moisture.

Temperature matters too. Concrete poured when ambient temperatures are below 40°F (4°C) or above 90°F (32°C) requires special measures. In summer pours across the Charlotte metro and Lake Norman area — where July temperatures regularly exceed 90°F — pour in the early morning, mist the subgrade before placing concrete, and apply a curing compound or wet burlap immediately after the bleed water disappears from the surface. Hot weather accelerates hydration and can cause rapid stiffening, crazing, and surface scaling if not managed.

For cold-weather pours in the North Carolina mountains near Hickory or Statesville, protect fresh concrete from freezing for at least 24 to 48 hours using insulating blankets. Concrete that freezes before reaching 500 PSI will suffer permanent structural damage that no amount of additional curing will correct.

If you are hiring a contractor rather than mixing bags yourself, make sure your contract specifies the curing method and duration. A professional concrete company should treat curing as standard practice, not an add-on. Learn more about how to hire a concrete contractor and what to look for in a written scope of work.

Frequently asked questions

How many bags of concrete do I need for a 10×10 slab?

A 10×10 slab at 4 inches thick requires approximately 50 bags of 80-pound concrete. The calculation is 10 × 10 × 0.333 = 33.3 cubic feet, divided by 0.60 = 55.5 bags, rounded up and buffered to about 50 after rechecking the math — always round up, never down. Add 10 percent for waste before purchasing.

How many 80-pound bags are in a cubic yard of concrete?

One cubic yard equals 27 cubic feet. An 80-pound bag yields 0.60 cubic feet, so you need 45 bags per cubic yard. For 60-pound bags yielding 0.45 cubic feet, the count is 60 bags per cubic yard. For 40-pound bags at 0.30 cubic feet, you need 90 bags per cubic yard.

Is it cheaper to buy bagged concrete or order ready-mix?

For volumes under 1 cubic yard, bagged concrete is usually more economical when you factor in the ready-mix minimum order and short-load fees. Above 1 cubic yard, ready-mix delivered in North Carolina typically runs $125 to $180 per cubic yard, versus roughly $293 in 80-pound bags plus mixing labor and equipment rental. Ready-mix also produces a more consistent mix design with a controlled water-cement ratio.

How thick should a concrete slab be?

Residential patios and sidewalks require a minimum of 4 inches. Vehicle-bearing driveways should be 4 to 6 inches, with 5 inches being the most common residential standard. Structural slabs, foundations, and pool decks typically require 6 inches or more depending on the load-bearing requirements specified in local building codes.

What PSI concrete should I use for a driveway?

The minimum recommended PSI for a residential driveway is 3,000, but 3,500 to 4,000 PSI is the better choice for longevity. In areas of North Carolina that experience freeze-thaw cycles — the Triad, Piedmont, and mountain regions — specify air-entrained concrete at 4,000 PSI to resist scaling and spalling from road salts and ice.

Can I mix concrete bags by hand for a large project?

Hand-mixing is practical for up to about 0.5 cubic yards, roughly 22 to 25 bags of 80-pound mix. Above that volume, an electric drum mixer or a ready-mix truck is a far better option. Inconsistent hand-mixing leads to variable water-cement ratios across the pour, creating weak spots that manifest as crazing, scaling, and early cracking.

How much water do I add to an 80-pound bag of concrete?

Most 80-pound bagged mixes call for approximately 3 quarts of water per bag; check the specific product label for the exact recommendation. Adding more water than directed is the most common DIY mistake: the ACI notes that excess water can reduce compressive strength by up to 600 PSI per additional quart per sack of cement. Mix until lump-free without exceeding the rated water amount.

How long does bagged concrete take to cure?

Bagged concrete typically reaches initial set in 1 to 2 hours and can support foot traffic after 24 to 48 hours. Full strength — typically 3,000 to 4,000 PSI — develops at 28 days under proper curing. Keeping the slab continuously moist for at least 7 days is the single most impactful step you can take to maximize final strength and reduce surface scaling.

Key takeaways

• Use the formula: Length × Width × Depth (in feet) ÷ bag yield × 1.10. An 80-pound bag yields 0.60 cubic feet; a 60-pound bag yields 0.45 cubic feet.
• For projects over 1 cubic yard, ready-mix delivery is almost always more cost-effective and produces a more consistent result than bagged concrete.
• North Carolina's clay soils and seasonal temperature swings require proper subgrade compaction, air-entrained mix in freeze-thaw zones, and a minimum 7-day moist cure.
• PSI matters: use 3,500 to 4,000 PSI for driveways, 3,000 PSI minimum for patios and sidewalks, and 4,000+ PSI for structural applications.
• Rebar or wire mesh reinforcement and proper control joint spacing prevent settlement cracking far more effectively than simply increasing bag count or slab thickness.
• Curing is the most-skipped and most-important step — proper curing for 7 days can be the difference between a slab that lasts 30 years and one that scales within 5.

Ready to get started? Pay nothing until the work is complete. Get a free concrete estimate — Local Concrete serves Charlotte, Raleigh, Winston-Salem, Greensboro, and surrounding North Carolina markets.