Exact material and waste-adjusted order volume stay separate. When you compare bags, the project total is rounded once for each bag size instead of adding already-rounded zone counts.
How the project total is calculated
Project order ft³ = sum of each valid zone order ft³; project yd³ = project order ft³ ÷ 27
Each slab or post-hole group keeps its own geometry and waste setting. Project exact volume sums exact slab volume and net post-hole volume. Project order volume sums the adjusted result from each zone.
For bags, count = ceil(project order ft³ ÷ configured yield). One ceiling operation on the combined project avoids the extra rounding created by buying every zone separately.
Worked example: one patio and two fence groups
A 10 ft × 12 ft × 4 in patio contributes 40.00 ft³ exact and 44.00 ft³ with 10% waste. Ten 12 in × 36 in holes contribute 23.56 ft³ exact and 25.92 ft³ with 10% waste. Four 9 in × 24 in holes contribute 3.53 ft³ exact and 3.71 ft³ with 5% waste.
The project total is 67.10 ft³ exact and 73.63 ft³ to order, or 2.73 yd³. At the editable 0.60 ft³ yield for an 80 lb bag, ceil(73.6291 ÷ 0.60) gives 123 bags. These values match the normative slab and multiple-group fixtures.
Assumptions kept visible
Concrete waste is editable for each zone and starts at 10%. Bag yields are editable planning presets reviewed on July 11, 2026; confirm the yield on the product you will purchase.
Only complete, valid zones contribute to a result. Gravel remains a separate material, and mixed gravel-density weights are never folded into the concrete total.
When to use this mode
Start here when the job includes more than one concrete area or repeated-hole group. Use the focused slab and post-hole pages when you want to work on one geometry in detail.
What this project mode does not decide
This mode does not schedule pours or advise on joints, strength, reinforcement, slab or footing depth, delivery minimums, labor, equipment, tax, or local requirements.
A combined quantity is not a recommendation to pour every zone at the same time or buy one particular product.
Sources and review dates
- Concrete Cal calculation method v1.0 · Reviewed 2026-07-11 · Planning method
- QUIKRETE concrete quantity calculator · Reviewed 2026-07-11 · Official source
- QUIKRETE Form-and-Pour product brochure · Reviewed 2026-07-11 · Official source