Concrete · Use case

How much concrete,
in cubic yards.

Enter the dimensions of your slab, patio, or footing. Get the concrete volume in cubic yards, cubic feet, and bags — with an automatic 10% overage allowance for spillage and uneven subgrade.

Bag mix vs ready-mix

When to call a truck.

Bagged concrete is fine for fence posts, small repairs, and projects under about half a yard. Beyond that, the labor and number of bags adds up fast:

  • Under 0.3 yd³ (~8 ft³): bagged is most economical.
  • 0.3 – 1.0 yd³: bagged works but you're mixing 25–60 bags.
  • Over 1 yd³: ready-mix delivery wins on labor and consistency.
  • Over 3 yd³: definitely ready-mix; most plants have a 1 yd³ minimum.

Ready-mix is usually priced per cubic yard with a delivery fee and short-load surcharge for orders under 5 yd³.

Bags per cubic yard
1 cubic yard27 ft³
80 lb bags45 bags
60 lb bags60 bags
40 lb bags90 bags

Always add 5–10% extra. Concrete waste from uneven ground is common.

Common slab sizes

Concrete needed by project.

Project Dimensions Concrete needed
Sidewalk section3 × 3 × 4 in3 ft³ · 0.11 yd³
Fence post hole10 × 10 × 36 in2 ft³ · 0.07 yd³
Shed pad8 × 8 × 4 in21 ft³ · 0.79 yd³
Patio10 × 12 × 4 in40 ft³ · 1.48 yd³
Single garage floor12 × 20 × 4 in80 ft³ · 2.96 yd³
Driveway (small)20 × 12 × 4 in80 ft³ · 2.96 yd³
Driveway (large)40 × 12 × 4 in160 ft³ · 5.93 yd³
Concrete FAQ

Common questions.

How much concrete do I need for a slab?
Multiply length × width × depth (all in feet) to get cubic feet, then divide by 27 for cubic yards. A 10×10 ft slab at 4 inches deep needs about 1.23 cubic yards of concrete.
How many bags of concrete equal a cubic yard?
It depends on bag size. An 80 lb bag yields about 0.6 ft³, so 45 bags make a cubic yard. A 60 lb bag yields about 0.45 ft³ (60 bags per yard), and a 40 lb bag yields about 0.3 ft³ (90 bags per yard).
Should I order extra concrete?
Yes — always add 5–10% extra to account for spillage, uneven subgrade, and waste. For a 1 yd³ pour, order 1.1 yd³; for a 5 yd³ pour, order 5.25 yd³. Ready-mix is usually delivered in half-yard increments.
What thickness should my slab be?
Walkways and patios: 4 inches. Driveways and shed pads: 4–6 inches. Garage floors: 4–6 inches with rebar. Heavy machinery or vehicles over 4 tons: 6+ inches with engineered reinforcement.
Related reading

From the blog.

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