Concrete volume.
Concrete volume for slabs, footings, and post holes with a waste-factor multiplier. Output in cubic yards, cubic meters, and bag count (60 lb and 80 lb).
How this works
Concrete volume is straightforward geometry:
Slab / footing: V = L × W × T Post hole / column: V = π × (D/2)² × H Total order = V × (1 + waste fraction)
Bag-count math
Pre-mixed concrete bags yield approximately:
- 60 lb bag: 0.45 ft³ (≈ 0.0127 m³) of finished concrete
- 80 lb bag: 0.60 ft³ (≈ 0.0170 m³)
- 40 lb bag: 0.30 ft³ (≈ 0.0085 m³)
Yield varies by manufacturer — Quikrete, Sakrete, and others publish slightly different numbers. The values above are typical for general-purpose concrete mix.
When to order ready-mix vs bags
The rough breakeven is about 1 cubic yard (≈ 27 ft³, ≈ 0.76 m³). Below that, bags are cheaper and you don't have ready-mix truck minimums to worry about. Above 1 cu yd, ready-mix becomes more economical and far faster (one truck delivers 8-10 cu yd vs ~60 bags per yard).
Common pitfalls
- Always order extra. Concrete can't be added partway through — once you've started pouring, you're committed. 10% waste is standard for rectangular pours; 15-20% for irregular shapes or anything below grade where the soil may absorb some.
- Footing dimensions vary by frost line and soil bearing capacity. The minimum thickness shown here is a typical residential value — check your local building code for required depth (frost line) and footing dimensions (soil-bearing).
- Bag concrete vs ready-mix have different strengths. Bag concrete is typically 4000 psi but can vary. Ready-mix is specified to your spec (3000, 4000, 4500 psi etc.) and tested.
- Don't forget reinforcement. Most concrete in modern construction includes rebar, wire mesh, or fiber reinforcement. The cost is separate from the concrete itself but should be planned together.
- Settle factor for post holes. Concrete compacts about 2-3% as it cures. For tall, narrow pours (post holes, columns), overfill slightly to compensate.
Sources
- Standard yield values: Quikrete and Sakrete bag specifications.
- Concrete mix design: ACI 211.1 — Standard Practice for Selecting Proportions for Normal, Heavyweight, and Mass Concrete.
- Residential foundations: ACI 332 / IRC Chapter 4 for foundations.
Disclaimer. This is a volume calculator for ordering material. Footing dimensions, depth, reinforcement, and structural requirements are governed by local code and should be designed by a qualified professional for any load-bearing application.