Concrete Estimating Without Guessing the Pour
Most DIY concrete mistakes start with volume, not finishing. This guide focuses on the geometry: feet × feet × inches → cubic yards—and how bag yield turns that volume into a shopping list.
Cubic Feet First, Then Yards
A rectangular slab is a prism. Convert thickness from inches to feet (divide by 12), multiply by length and width, then divide by 27 to get cubic yards—the unit ready-mix plants quote.
Waste Is Not Optional Polish
Uneven subgrade, form bulge, and cleanup eat volume. A 5–10% waste allowance on slabs is a common DIY habit. Skipping it is how pours run short at the worst moment.
Bag yield beats bag weight
An “80 lb bag” is a shipping size. Coverage depends on the yield printed on the label (often near 0.60 cu ft when mixed). Always divide volume by yield, then round up.
Bags vs Ready-Mix
Bags suit small pads and repairs. Once you cross roughly a cubic yard—or several dozen heavy bags—ready-mix delivery usually wins on labor and consistency.