Post displacement is optional and explicit. When enabled, gross hole volume and the volume subtracted for the post remain visible beside net concrete.
Cylindrical holes with optional displacement
Gross group ft³ = π × (diameter ÷ 2)² × depth × count; net = gross − explicit post displacement
A round post uses π × post radius² × embedded depth per hole. A rectangular post uses width × thickness × embedded depth per hole. The group order volume is net exact volume times one plus waste.
If displacement is off, it is exactly zero. Embedded depth greater than hole depth and a post cross-section equal to or larger than the hole are rejected rather than silently adjusted.
Worked example: ten holes with square-post displacement
For ten 12 in diameter × 36 in deep holes, gross per hole is π × 0.5² × 3 = 2.3562 ft³ and gross group volume is 23.5619 ft³.
A 4 in × 4 in post embedded 36 in displaces 0.3333 ft³ per hole, leaving 20.2286 ft³ net exact. With 10% waste the order volume is 22.2515 ft³. Editable presets produce 75 × 40 lb, 50 × 60 lb, or 38 × 80 lb bags. These are normative Fixture C values.
Group and displacement assumptions
Count must be a positive integer. Waste begins at 10%. Displacement starts off; when enabled, shape, post dimensions, and embedded depth are explicit inputs.
Different hole dimensions belong in separate groups so every subtotal remains traceable before the project total is calculated.
Why groups matter
Keep gate posts, line posts, or other differently sized sets in separate groups. Concrete Cal totals their valid net and adjusted quantities while preserving each group's inputs and assumptions.
Enter dimensions from your own plan
Concrete Cal does not choose hole diameter, hole depth, embedment, post spacing, or bag product. It does not provide frost, load, footing, soil, drainage, auger, installation, or code advice.
The result estimates fill volume only. Confirm every project dimension through your plans, local requirements, product instructions, or a qualified professional.
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