Concrete Mix Calculator
Estimate ready-mix concrete volume and bag count for a rectangular pour.
Calculate your estimate
Planning estimate only. Verify manufacturer specifications, local codes and project measurements.
Enter slab dimensions and the bag’s stated yield
- Measure the rectangular pour in feet for length and width. Enter concrete depth in inches, not feet.
- Read the mixed-volume yield on the specific premix bag. Enter cubic feet per bag; bag weight alone is not the yield.
- Select Calculate to see whole bags and cubic yards. Split irregular pours into rectangles and add their unrounded volumes before ordering.
Concrete Mix Calculator: formula and assumptions
Volume (ft³) = length × width × depth in inches ÷ 12. Bags = volume ÷ stated bag yield, rounded up. Cubic yards = cubic feet ÷ 27.
Worked calculation
12 × 10 × 4 ÷ 12 = 40 ft³ = 1.48 yd³. At 0.6 ft³ per bag, order 67 bags before any extra allowance.
What this estimate includes
This estimates packaged premix bags, not cement/sand/aggregate mixing ratios. Use the yield on your bag; no waste allowance is included.
Planning details that change the estimate
The output is the theoretical volume of a rectangular pour with no built-in waste. Account separately for uneven excavation, spillage and other project allowances. Compare packaged concrete with ready-mix using volume, delivery and placement requirements rather than assuming bags are always the practical choice. The tool does not select concrete strength, reinforcement, curing methods or a cement-to-sand mixing ratio.
Concrete Mix Calculator FAQs
Does this calculate a cement, sand and aggregate ratio?
No. It estimates bags of premixed concrete using a stated yield, not the proportions for a site-batched mix.
Can I use a different bag size?
Yes. Replace bag yield with the mixed-volume yield for that product. Do not enter the bag’s weight in the yield field.
Is waste included?
No. The visible inputs contain no waste percentage. Apply your project allowance separately and avoid adding the same allowance twice.
Why are bags rounded up?
Concrete is purchased in whole bags. A fractional requirement is rounded to the next full bag, while cubic yards remains a volume estimate.
Continue planning this project
For a slab estimate with an explicit waste allowance, use the Concrete Slab Calculator. Estimate strip foundations with the Concrete Footing Calculator and isolated cylindrical pours with the Post Hole Concrete Calculator.
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