ConcreteYardCalc

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Avg. range: $130 - $160

Rectangle Slab

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Quick Estimate Tip: The Magic Number 81

For a 4-inch thick slab, you can quickly estimate cubic yards by dividing the total square footage by 81.

Square Feet ÷ 81 = Cubic Yards

Example: A 200 sq ft slab needs about 2.47 cubic yards (200 ÷ 81)

What the Pros Say: Concrete Estimating Tips

Never Order the Exact Amount

Always include a safety margin. Coming up short is far more expensive than having a little left over.

Add 1/4" to Thickness for Budget

Assumes proper grading and compaction. This buffer accounts for variations in subgrade.

Transform Odd Shapes to Rectangles

For driveways, use the average width. A 16' top and 12' bottom averages to 14' — close enough!

Call Your Ready-Mix Plant

Give them your square footage and thickness — they'll verify your calculations for free.

Frequently Asked Questions

How do I calculate how much concrete I need?
Use our concrete calculator or the formula: Length × Width × Thickness. Measure in feet and inches, multiply the dimensions to get cubic feet, then divide by 27 to convert to cubic yards.
What is the standard thickness of concrete?
  • 4 inches — Standard for patios, walkways, and residential driveways
  • 5-6 inches — Garage floors and heavy-duty driveways
  • 6-8 inches — Commercial applications
How much does 1 yard of concrete weigh?
A solid slab of concrete weighs approximately 4,000 pounds (2 tons) per cubic yard. Broken concrete weighs about half that — around 2,000 pounds.
How many bags of concrete for 1 yard?
To produce 1 cubic yard of concrete, you'll need approximately:
  • 60 bags of 60lb concrete
  • 45 bags of 80lb concrete
Bagged concrete or ready-mix delivery?

Use ready-mix delivery for larger projects like driveways, patios, foundations, and slabs over 2 cubic yards.

Use bagged concrete for smaller projects like repairs, footings, small pads, fence posts, and steps.

What's the minimum order for ready-mix?
Most ready-mix suppliers have a minimum order of 1 cubic yard per delivery. Anything less may incur a short-load fee.
How much extra should I order?
Add 10-15% extra to your order to account for spillage, uneven subgrade, and variations. Coming up short causes delays, extra delivery charges, and potential quality issues with cold joints.