Estimate concrete bags and optional gravel for round post holes using user-provided hole, post, and base dimensions.
The calculator finds cylindrical hole volume, separates any gravel-base zone, optionally subtracts post displacement within the concrete zone, and then applies project waste once.
It estimates materials only and does not select hole diameter, embedment, frost depth, or structural footing requirements.
hole volume = π × (diameter ÷ 2)² × depthconcrete depth = hole depth − gravel depthnet concrete = concrete-zone volume − embedded post volumebags = ceil(net concrete × (1 + waste rate) ÷ manufacturer yield)gravel bags = ceil(gravel volume × (1 + separate gravel waste) ÷ gravel bag yield)A 12 in diameter, 36 in deep round hole uses the shared cylinder engine; exact displayed conversions come from the common volume system.
Four identical holes multiply the unrounded per-hole volume before the project concrete allowance is applied.
With a 6 in gravel base in a 36 in hole, gravel occupies the bottom 6 in and the gross concrete zone is 30 in deep.
A 300 mm diameter, 900 mm deep group uses the same canonical-meter geometry as US units.
Hole width, depth, embedment, and frost requirements must come from the design, local conditions, and applicable codes.
Concrete bag weight does not determine mixed yield; enter the product’s stated volume per bag.
Ignoring post displacement is more conservative; including it can matter when the post is large relative to the hole.
Gravel has its own depth, waste, yield, and price assumptions.
Diameter and depth are converted to meters before the shared cylinder formula is evaluated. Hole groups retain full precision until project totals are summed.
Round and rectangular post cross-sections are supported. Displacement is limited to entered embedment within the concrete zone. Fit validation is geometric only.
Gravel occupies the bottom of the hole. The default assumption is that the post displacement begins above the gravel material zone.
Concrete waste is applied once after group totals. Whole bags use shared yield-based purchase rounding.
Groups can represent fence, corner, gate, deck, pergola, mailbox, or sign posts with different dimensions and quantities.
Concrete and gravel bag costs are calculated separately and combined. Posts, labor, equipment, reinforcement, delivery, tax, and disposal are excluded.
Calculate the cylindrical concrete-zone volume, subtract optional embedded post displacement, add project extra, and divide by bag yield.
Multiply the circular cross-sectional area by hole depth.
Divide net concrete per hole by manufacturer yield; project purchasing should use the total whole-bag result.
Enter the project-specified hole dimensions and number of fence posts.
Enter dimensions from the approved footing design; this calculator only estimates volume.
It is optional. Ignoring displacement is more conservative, while including it may refine quantities for larger posts.
This calculator does not prescribe construction details. Enter gravel only when required by your project.
Gravel reduces concrete-zone depth and is calculated as a separate material volume.
Multiply exact per-hole volume by quantity or create multiple groups for different holes.
The calculator does not determine depth; consult project design, site conditions, frost requirements, and codes.
The calculator does not determine diameter or structural clearance.
No. Frost depth is location- and code-dependent.
No. It does not assess loads, capacity, reinforcement, uplift, lateral resistance, or code compliance.