Methods, Sources & Assumptions
A rectangular form uses length × width × thickness. A cylinder uses π × diameter² ÷ 4 × height. For a round post inside a round hole, its same-depth cylinder is subtracted. The identical-form count multiplies volume before the allowance. Measurements are converted consistently before multiplication.
Bags = adjusted concrete volume ÷ the specific product’s mixed yield, rounded up. Named product yields are approximate manufacturer figures, not universal bag-weight conversions. Ready-mix volume is rounded separately to your entered order increment.
Worked check: a 12 × 10 ft slab at 4 in is 40 ft³. With 10% allowance it is 44 ft³, or 1.62963 yd³. At 0.60 ft³ per bag, the result is 74 bags. A quarter-yard bulk increment gives 1.75 yd³. These inputs do not establish a suitable structural design.
What the result means
Results are planning estimates. Unrounded values are used in the calculations; rounding is applied for display and whole purchasing units. Changing the unit system resets example values rather than silently treating old numbers as different units. The calculator rejects invalid dimensions and impossible combinations.
Sources
- QUIKRETE Concrete Mix No.1101 — Technical data sheet
- NIST Guide to SI, Appendix B.8 — Conversion factors
- SAKRETE PRO-X180 Rapid Strength Concrete Mix — Technical data sheet
Corrections
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