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Matemática & Medidas4 min•2026-10-29•Compute-Hub Math & DIY Desk
How to Calculate Concrete: Cubic Yards & Cubic Meters Guide
Estimating materials for slabs, footings, post holes, and gravel projects with waste margins.
Key Takeaways
- Formula: Volume in Cubic Yards = (Length in ft × Width in ft × Thickness in inches) / 324.
- Metric: Volume in Cubic Meters = Length (m) × Width (m) × Depth (m).
- Always add 10% extra for subgrade unevenness, spillage, and formwork deflection.
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The 324 Shortcut Formula for Slabs
When ordering ready-mix concrete in the US, dimensions are typically given in feet for length and width, but inches for slab thickness. Instead of converting inches to fractions of feet, divide the product by 324 to get cubic yards instantly.
Mathematical Formula:Cubic Yards = (Length_ft × Width_ft × Depth_inches) / 324 × 1.10 (with 10% waste)
💡 Practical Real-World Example:A 20 ft by 10 ft patio slab at 4 inches thick: (20 × 10 × 4) / 324 = 800 / 324 = 2.47 cubic yards. Adding 10% buffer equals 2.7 cubic yards.
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Frequently Asked Questions
FAQ: How to Calculate Concrete: Cubic Yards & Cubic Meters Guide
How many 80 lb bags of concrete make one cubic yard?
It takes approximately 45 bags of 80 lb ready-mix concrete to make one full cubic yard.