Concrete / Post holes & bags
Concrete Fence Post Calculator
Calculate concrete for circular fence-post holes in cubic metres, cubic feet, or cubic yards. Deduct the post, combine different hole groups, and estimate whole bags from the manufacturer’s stated yield.
Estimate concrete for post holes
Enter each post-hole group and optional post displacement, then compare net volume with practical whole-bag plans.
Allowance, bags and cost — optional
Blank means 0%. Choose an allowance for the actual holes and placement plan.
Copy the yield from the exact product label; bag mass alone does not establish yield.
This selection changes bag-priced cost only. Both bag totals remain visible.
Enter a volume rate or price per bag; leave blank for quantities only.
The currency label does not fetch local prices or convert exchange rates.
Concrete quantities
- Total post holes
- 10 holes
- Gross hole volume
- 0.4241150082 m³
- Post displacement
- 0.06 m³
- Net concrete volume
- 0.3641150082 m³
- Net concrete in cubic feet
- 12.85860016 ft³
- Allowance volume
- 0 m³
- Estimated ordering volume
- 0.3641150082 m³
- Estimated order in yards
- 0.4762444505 yd³
Whole-bag plans
- Exact calculated bags
- —
- Minimum when material is pooled
- —
- Plan using whole bags per hole
- —
- Additional bags from per-hole rounding
- —
Concrete material cost
- Estimated material cost
- —
View post-hole group breakdown
Group 1
- Holes
- 10
- Net concrete per hole
- 0.03641150082 m³
- Group net concrete
- 0.3641150082 m³
- Exact bags per hole
- —
- Whole bags per hole
- —
View copyable summary
ConstructGauge — Concrete Fence Post Calculator Post-hole groups: 1; total holes: 10 Gross hole volume: 0.4241150082 m³ Post displacement: 0.06 m³ Net concrete: 0.3641150082 m³ / 12.85860016 ft³ Allowance (0%): 0 m³ Estimated order: 0.3641150082 m³ / 0.4762444505 yd³ Quantity estimate only. Enter dimensions required by the project. Does not size post holes or verify fence, footing, soil, frost, wind, structural, or code requirements.
Method
How to calculate concrete for fence-post holes
Enter the actual diameter of each circular hole and the depth that will contain concrete. The calculator finds the cylindrical hole volume, subtracts the volume occupied by the post, and multiplies the result by the number of identical holes.
- Hole area = π × (hole diameter ÷ 2)²
- Post area = π × (post diameter ÷ 2)² for a round post, or width × length for a rectangular post
- Net concrete per hole = (hole area − post area) × concrete-filled depth
- Project net concrete = sum of each group’s net volume × hole count
- Ordering volume = net concrete + user-selected allowance
- Exact bag quantity = ordering volume ÷ manufacturer yield per bag
All dimensions are converted to metres internally. Displayed values are rounded; the calculation retains the underlying values. Whole-bag outputs appear only when you enter a positive cured-volume yield from the exact product.
Worked example
Ten 300 mm holes with 100 mm square posts
For a 300 mm diameter hole with 600 mm of concrete depth, the gross cylindrical volume is approximately 0.0424115 m³. A centered 100 × 100 mm post displaces 0.006 m³, leaving 0.0364115 m³ per hole.
Ten identical holes require 0.364115 m³ net. A chosen 5% allowance adds approximately 0.0182058 m³, producing an estimated order of 0.382321 m³. With a manufacturer yield of 10 L per bag, the project needs a minimum of 39 pooled bags or 40 bags when every hole receives a separately rounded four-bag allocation.
Minimum pooled bags versus whole bags per hole
The pooled minimum rounds the complete project quantity upward once. It is the mathematical minimum when material can be measured and shared across holes. The per-hole plan rounds each hole upward before multiplying by its group count, which can require more bags.
The calculator shows both figures instead of deciding how you must mix or distribute the product. If you enter a price per bag, choose the plan that matches your intended purchase. Follow the manufacturer’s directions for whole-bag mixing, water, handling, and placement.
Line, corner, end, and gate posts
Use one group only when the hole diameter, concrete-filled depth, and post cross-section are identical. Add another group for corner, end, or gate posts with different entered dimensions. This preserves the quantity for each group instead of hiding differences inside an average.
The calculator does not determine how many posts a fence needs. Count posts from the approved layout, including endpoints, corners, changes of direction, and gates as applicable to the project.
Choosing the measurements
Hole diameter describes the excavated circular opening, while post width or diameter describes the material occupying its center. Use actual post dimensions rather than relying on a nominal label. The post must fit inside the entered hole and leave a positive concrete cross-section.
Concrete-filled depth means only the vertical depth occupied by concrete. If part of the hole contains another material, exclude that portion from this input. This tool calculates neither that other material nor whether it is suitable for the installation.
Using the result in a BOQ or purchase plan
Use net concrete volume as the direct geometric BOQ quantity and keep post displacement visible as a deduction. Record ordering allowance separately. Bag rounding and material cost are procurement outputs and should not replace the net concrete quantity.
The optional rate covers concrete material only. It excludes excavation, spoil disposal, posts, reinforcement, labor, equipment, delivery, taxes, and other fence work. The currency selector labels your rate and does not fetch prices or convert exchange rates.
Concrete fence post calculator FAQ
How many bags of concrete do I need per fence post?
It depends on the entered hole diameter, concrete depth, post displacement, allowance, and the exact product yield. Enter those values to see the unrounded bags per hole, whole bags per hole, and total project plans.
Does the calculator subtract the fence post?
Yes, when you select a round, square, or rectangular post and enter its actual dimensions. Select no deduction if you intentionally need the full cylindrical hole volume.
Can I use this as a postcrete calculator?
Yes, when the product label provides a cured-volume yield per bag. Enter that yield directly. The calculator does not assume that every post-setting or premixed concrete product has the same yield.
Does it calculate concrete for 4×4 posts?
Enter the actual measured post width rather than assuming the dimensions from the nominal name. The result depends on the actual hole and post geometry.
Can I account for material beneath the concrete?
Enter only the concrete-filled depth. Any part of the hole occupied by another material is therefore excluded, but this calculator does not estimate or recommend that material.
Does this tell me how deep or wide to make the hole?
No. Required dimensions can depend on the fence, loads, post system, soil, climate, frost conditions, local rules, and project design. Obtain them from the applicable project requirements.
Can I use it for deck posts or structural piers?
The geometry can calculate concrete around a known embedded post, but it does not design or approve a structural footing. Use the dimensions and details established for that project.
Calculation basis and source limits
The calculation uses cylinder and cross-sectional geometry, percentage arithmetic, and manufacturer-yield division. It does not establish installation instructions, concrete performance, structural capacity, or product suitability.
Metric and Imperial conversions use international feet, inches, and yards. See NIST’s SI conversion-factor reference for the unit basis. NIST does not certify this calculator or its construction assumptions.