How Many Square Feet Will a Bag of Concrete Cover?

If you’re pouring a patio, repairing a sidewalk, or installing fence posts, you may wonder: How many square feet will a bag of concrete cover?

The answer depends on two things:

• The size of the concrete bag.
• The thickness of the slab.

For example, an 80-pound bag of concrete covers about 4 square feet at a thickness of 4 inches.

Smaller bags cover less area, while thinner slabs cover more area.

In this guide, you’ll learn how to calculate concrete coverage and see charts for the most common bag sizes.

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Quick Answer: How Many Square Feet Does a Bag of Concrete Cover?

Here is the approximate coverage at 4 inches thick:

Bag Size	Coverage
40-pound bag	2 square feet
50-pound bag	2.5 square feet
60-pound bag	3 square feet
80-pound bag	4 square feet

These numbers are estimates and may vary slightly by manufacturer.

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What Determines Concrete Coverage?

Concrete coverage depends on:

• Bag weight.
• Concrete mix.
• Slab thickness.
• Waste during installation.

A thicker slab uses more concrete, which means the bag covers fewer square feet.

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Concrete Coverage Formula

To estimate coverage, use the following formula:

You must first convert the slab thickness from inches to feet.

For example:

• 4 inches = 0.333 feet

Then divide the bag’s volume by the thickness.

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Coverage Chart for Common Concrete Bag Sizes

Coverage at 2 Inches Thick

Bag Size	Coverage
40-pound bag	4 sq ft
50-pound bag	5 sq ft
60-pound bag	6 sq ft
80-pound bag	8 sq ft

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Coverage at 3 Inches Thick

Bag Size	Coverage
40-pound bag	2.7 sq ft
50-pound bag	3.3 sq ft
60-pound bag	4 sq ft
80-pound bag	5.3 sq ft

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Coverage at 4 Inches Thick

Bag Size	Coverage
40-pound bag	2 sq ft
50-pound bag	2.5 sq ft
60-pound bag	3 sq ft
80-pound bag	4 sq ft

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Coverage at 6 Inches Thick

Bag Size	Coverage
40-pound bag	1.3 sq ft
50-pound bag	1.7 sq ft
60-pound bag	2 sq ft
80-pound bag	2.7 sq ft

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How Much Concrete Is in Each Bag?

The volume of concrete varies by bag size.

Bag Size	Approximate Volume
40-pound bag	0.30 cubic feet
50-pound bag	0.37 cubic feet
60-pound bag	0.45 cubic feet
80-pound bag	0.60 cubic feet

Manufacturers may list slightly different yields.

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Common Projects and Recommended Thickness

Different projects require different slab depths.

Project	Recommended Thickness
Sidewalk	4 inches
Patio	4 inches
Shed base	4–5 inches
Driveway	5–6 inches
Garage floor	6 inches

Always follow local building codes and manufacturer instructions.

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How Many Bags Do You Need for Common Projects?

10 × 10 Patio (100 Square Feet)

At 4 inches thick:

• Approximately 25 bags of 80-pound concrete.

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12 × 12 Slab (144 Square Feet)

At 4 inches thick:

• Approximately 36 bags of 80-pound concrete.

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20 × 20 Driveway (400 Square Feet)

At 4 inches thick:

• Approximately 100 bags of 80-pound concrete.

Large projects are often more economical with ready-mix concrete.

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Should You Buy Extra Concrete?

Yes. Most contractors recommend buying:

• 5–10% extra concrete.

Extra material helps account for:

• Spills.
• Uneven ground.
• Measuring errors.
• Waste.

Running out of concrete during a pour can create problems.

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Bagged Concrete vs. Ready-Mix Concrete

Type	Best For
Bagged concrete	Small projects
Ready-mix concrete	Large projects

Bagged concrete works well for:

• Fence posts.
• Small patios.
• Steps.
• Repairs.

Ready-mix is usually better for driveways and foundations.

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FAQs

How many square feet does an 80-pound bag of concrete cover?

An 80-pound bag covers approximately 4 square feet at 4 inches thick.

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How many square feet does a 60-pound bag cover?

A 60-pound bag covers approximately 3 square feet at 4 inches thick.

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Does slab thickness affect coverage?

Yes. Thicker slabs reduce the area covered by each bag.

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How many bags of concrete do I need for a 100-square-foot slab?

At 4 inches thick, you’ll need about 25 bags of 80-pound concrete.

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Is bagged concrete cheaper than ready-mix?

Bagged concrete is often cheaper for small projects, while ready-mix is more cost-effective for larger jobs.

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Should I buy extra concrete?

Yes. Experts recommend purchasing 5–10% extra.

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How do I calculate concrete coverage?

Divide the bag’s concrete volume by the slab thickness.

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Quick Facts

• Coverage depends on bag size and slab thickness.
• An 80-pound bag covers about 4 square feet at 4 inches thick.
• A 60-pound bag covers about 3 square feet at 4 inches thick.
• Thicker slabs require more concrete.
• Most projects need extra material for waste.

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Final Thoughts

The number of square feet a bag of concrete covers depends on the bag size and the thickness of the slab. At a standard depth of 4 inches, an 80-pound bag covers about 4 square feet, while smaller bags cover less area.

Knowing these estimates can help you plan your project, budget accurately, and avoid running out of concrete during installation.

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