Concrete Calculator — Cubic Yards & Bag Estimator
Precisely calculate volume for slabs, footings, and columns. Estimate ready-mix truck loads or individual bags for smaller projects.
One cubic yard of concrete equals 27 cubic feet. For a standard 4-inch slab, one cubic yard covers approximately 81 square feet. If using 80lb bags, you need 45 bags to make one cubic yard.
Concrete Coverage Reference
| Slab Depth | Yards per 100 sq.ft | Sq.ft per Cubic Yard |
|---|---|---|
| 4 Inches | 1.23 yd³ | 81 ft² |
| 5 Inches | 1.54 yd³ | 65 ft² |
| 6 Inches | 1.85 yd³ | 54 ft² |
| 8 Inches | 2.47 yd³ | 40 ft² |
How to Calculate Concrete Volume and Yield
Whether you are pouring a structural foundation, a residential driveway, or setting fence posts, accurate concrete estimation is critical to project success. Ordering too little concrete results in "cold joints" and structural weakness, while ordering too much leads to expensive environmental disposal fees. This calculator uses standard cubic geometry (Length × Width × Depth) to determine the exact volume required in cubic yards.
Ready-Mix Concrete vs. Bagged Concrete
For large pours (typically over 1.5 cubic yards), contractors order "ready-mix" concrete delivered by a mixer truck. Ready-mix is ordered in cubic yards. For smaller projects like footings, sidewalk repairs, or post holes, pre-mixed bags (such as Quikrete or Sakrete) are more economical. The yield of standard bagged concrete is heavily standardized:
- 80 lb bag: Yields exactly 0.60 cubic feet (requires 45 bags per cubic yard).
- 60 lb bag: Yields exactly 0.45 cubic feet (requires 60 bags per cubic yard).
- 50 lb bag: Yields exactly 0.37 cubic feet (requires 72 bags per cubic yard).
The Importance of Waste Factors
Never order the exact mathematical volume of a slab. Subgrades are rarely perfectly level, forms can bow under the hydraulic pressure of wet concrete, and some material will always be lost in the pump hose or truck chute. Industry standard dictates adding a 5% to 10% waste factor to your total calculation. For example, if a driveway mathematically requires 8.2 cubic yards, an experienced finisher will order 9 cubic yards.
ACI 318 Durability and Psi Standards
Volume is only one part of the equation; strength is the other. The American Concrete Institute (ACI 318) provides strict guidelines for compressive strength (PSI). A standard residential sidewalk may only require a 2500 PSI mix, whereas a garage slab subjected to vehicular loads and freeze-thaw cycles typically requires a 4000 PSI air-entrained mix.