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.
The initial dimensions are editable example starting values, not recommended hole geometry. This tool estimates materials only and does not select diameter, depth, 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)Using the editable 12 in diameter and 36 in depth inputs, one round hole has 2.356 ft³ of gross and net concrete volume when gravel and post displacement are off. With 10% extra and a user-entered 0.5 ft³ yield per bag, the calculator shows 2.592 ft³ planning volume, 5.18 exact bags, and 6 bags to buy.
Four identical 12 × 36 in holes total 9.425 ft³ before extra material. With 10% extra and 0.5 ft³ yield per bag, the result is 10.367 ft³ planning volume, 20.73 exact bags, and 21 bags to buy.
For one 12 in diameter, 36 in deep hole with a user-entered 6 in gravel base, gravel volume is 0.393 ft³ and the 30 in concrete zone is 1.963 ft³ before any post displacement or extra material.
One 300 mm diameter, 900 mm deep hole has 0.063617 m³ of gross volume, using the same canonical-meter geometry as US inputs.
Hole width, depth, embedment, and frost requirements must come from the design, local conditions, and applicable codes; do not treat the initial values as a recommendation.
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 calculator assumes that post displacement begins above the gravel material zone; it does not recommend whether gravel should be used.
Concrete waste is applied once after group totals. Whole bags use shared yield-based purchase rounding from the manufacturer yield supplied by the user.
Extension guidance illustrates that post setting can vary with fence type, soil, moisture, frost action, and loads. The calculator therefore leaves diameter, depth, and embedment to the project design rather than treating its editable starting values as universally sufficient.
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.