How many bags of concrete do I need?

An 80-lb bag of concrete yields approximately 0.60 cubic feet. A 60-lb bag yields about 0.45 cubic feet. To find the number of bags, divide your total cubic feet by the yield per bag. For larger pours, ready-mix concrete ordered by the yard is almost always more economical than bags.

When should I use bags vs. ready-mix concrete?

Use bags for projects under 1 cubic yard — fence posts, small footings, repairs, and small slabs. Order ready-mix for anything larger. Ready-mix is more cost-effective above about 1 yard, ensures a consistent mix, and eliminates the labor of mixing dozens of bags.

Concrete Calculator — Yards, Bags & Cost

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Concrete Volume Calculator

Choose your pour type, enter dimensions, and get cubic yards, bag count, and a cost estimate in seconds.

Length (ft)

Width (ft)

Thickness (in)

Length (ft)

Width (in)

Depth (in)

Diameter (in)

Depth (ft)

Number of holes

Waste factor

Ready-mix price ($/yd³)

Your Estimate

Cubic Yards

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with waste factor

Cubic Feet

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with waste factor

80-lb Bags

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bags needed

60-lb Bags

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bags needed

Ready-Mix Cost

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material only, est.

Net Volume

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cubic yards (no waste)

Concrete Thickness by Application

Application	Recommended Thickness	Notes
Sidewalk / Walkway	4 inches	Standard for pedestrian foot traffic.
Patio	4 inches	4" is sufficient for outdoor furniture and foot traffic.
Residential Driveway	5–6 inches	5" for passenger vehicles; 6" if trucks or RVs will park on it.
Garage Floor	4–6 inches	4" minimum; 6" if storing heavy equipment.
Footing (residential)	8–12 inches deep	Depends on local frost depth and load. Check local code.
Fence Post (tube)	10" diameter × 3× post depth	General rule: hole depth = 1/3 post height above grade.

Bags vs. Ready-Mix — the cutoff For pours under 0.5 cubic yards (about 27 cubic feet), bags are often the practical choice — no minimum order, no scheduling. Above 1 cubic yard, ready-mix is almost always cheaper per cubic foot and requires far less labor. Between 0.5 and 1 yard, it depends on your access to a mixer and how many bags you want to haul.

Frequently Asked Questions

How do I calculate how much concrete I need?

Multiply length × width × depth (all in feet) and divide by 27 to get cubic yards. For a 10×10 slab at 4 inches thick: 10 × 10 × 0.333 ÷ 27 = 1.23 cubic yards. Always add 10% for waste and overflow.

How many 80-lb bags make a cubic yard?

An 80-lb bag of concrete yields approximately 0.60 cubic feet. One cubic yard equals 27 cubic feet, so you need about 45 bags of 80-lb concrete per yard. A 60-lb bag yields 0.45 cubic feet, requiring about 60 bags per yard.

How thick should a concrete slab be?

4 inches is the standard for most residential slabs — patios, sidewalks, and garage floors. Driveways should be 5 to 6 inches, especially if trucks or larger vehicles will use them. Always check local building codes for footings and structural applications.

When should I order ready-mix vs. use bags?

Use bags for projects under 1 cubic yard — small slabs, fence posts, and footings. Order ready-mix for anything larger. Above 1 yard, ready-mix is more cost-effective and far less labor. Most suppliers have a minimum order of 1 yard.

Concrete Calculator —Yards, Bags & Cost

Concrete Thickness by Application

Frequently Asked Questions

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Concrete Calculator —
Yards, Bags & Cost