Fence Post and Post Hole Concrete Calculator
Enter a post hole's diameter and depth, the gravel base and the post, and get the bags of concrete for each hole and for the whole fence, with the gravel counted on its own line.
Estimates for planning, not professional advice. Read the full notice.
Example: one fence post hole
3 80 lb bags
- Concrete around the post 1.15 ft³
- To mix, with waste 1.27 ft³
- Gravel for the base 0.01 yd³
Estimate for planning, from what you entered and the product data shown. Check product labels and your supplier before you buy.
Your project
Enter a size to see your total.
Each product is rounded up once for the whole project, so the total can be less than the items bought alone added together. A line counted from a cut layout (sheets, boards or tiles laid out piece by piece) is counted for each item and added.
Shopping list
| Item | Size | Buy |
|---|---|---|
| Concrete mix | 80 lb bag | 3 |
| Gravel for the base | 1 yd³ | 0.5 yd³ |
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Worked example: one fence post hole
Show the working
- Area of the hole 3.1416 × 10 in × 10 in ÷ 4 = 78.54 in²
- Area of the post 3 1/2 in × 3 1/2 in = 12.25 in²
- Concrete area around the post 78.539816 in² − 12.25 in² = 66.29 in²
- Concrete depth 3 ft − 6 in[1] = 2 ft 6 in
- Concrete in the hole 66.289816 in² × 2 ft 6 in = 1.15 ft³
- Add the waste allowance 1.150865 ft³ + 10%[2] = 1.27 ft³
- Divide by the bag's yield 1.265951 ft³ ÷ approx. 0.6 ft³[3] = 2.11 bags
- Round up once, to whole bags 2.11 bags = 3 × 80 lb bags
Assumptions
The figures behind the example. Sourced figures link to their source below; a default is a starting value to check against your label or supplier.
| Assumption | Value | Details and changes |
|---|---|---|
| Concrete waste allowance | 10%[2] | |
| Default 10% is the top of NRMCA's 4% to 10% range. | ||
| Yield of the 40 lb bag | approx. 0.3 ft³[3] | |
| A 40 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
| Yield of the 50 lb bag | approx. 0.375 ft³[3] | |
| A 50 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
| Yield of the 60 lb bag | approx. 0.45 ft³[3] | |
| A 60 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
| Yield of the 80 lb bag | approx. 0.6 ft³[3] | |
| An 80 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
| Yield of the 90 lb bag | approx. 0.675 ft³[3] | |
| A 90 lb bag of QUIKRETE Concrete Mix 1101 yields about this many cubic feet, as the maker's own sheet states. | ||
Feet and inches, like 12' 6"
Bags for several posts: mixed across holes or whole bags per hole
80 lb bags for the example post, counted across all the holes and as whole bags for each hole, with the waste allowance added
| Posts | Mixed across the holes | Whole bags for each hole |
|---|---|---|
| 1 | 3 × 80 lb bags | 3 × 80 lb bags |
| 5 | 11 × 80 lb bags | 15 × 80 lb bags |
| 10 | 22 × 80 lb bags | 30 × 80 lb bags |
| 20 | 43 × 80 lb bags | 60 × 80 lb bags |
The calculator counts across all the holes, rounding up once. Mixing each hole from whole bags can need more.
The gravel base, a separate line
Gravel for the base of the example post holes, in cubic yards before the supplier's step, by number of holes
| Posts | Gravel base |
|---|---|
| 1 | 0.01 yd³ |
| 5 | 0.05 yd³ |
| 10 | 0.1 yd³ |
| 20 | 0.2 yd³ |
Gravel is its own line in the shopping list, ordered by the cubic yard. The base depth is the maker's figure and is an input you can change.
What the maker's post-setting sheet says about the base
The gravel base the maker's setting-posts sheet adds to the hole depth
| Figure | Maker's sheet |
|---|---|
| Gravel base added to the hole depth | 6 in |
Figures in the Maker's sheet column are per QUIKRETE's project sheet, checked Nov 12, 2026.
Product names are trademarks of their owners. HoneyDoMath is not affiliated with, sponsored by or endorsed by these makers. Figures come from each maker's published sheets and are shown for information only.
Source: [1]
This is manufacturer guidance, quoted in the sources below. It is not a sizing rule.
Questions
How many bags of concrete per fence post?
It depends on the hole and the post. The example above works one hole out step by step, and the table shows how the count grows across several posts. Enter your own sizes for your own count.
Does the post's volume come out?
Yes. The calculator subtracts the post's own area from the hole, so the concrete is only what fills around it. Enter the post's actual size, which is smaller than its nominal size.
Why a gravel base under the post?
The maker's setting-posts sheet, quoted in the sources, adds a gravel base to the hole depth. The calculator takes that depth out of the concrete and lists the gravel as its own line.
Is mixing across holes different from whole bags for each hole?
The table compares the two ways: mixing across all the holes rounds up once, while whole bags for each hole round up for every hole. The calculator shows the first and the table shows both.
Sources (3)
-
QUIKRETE Setting Posts project sheet (opens in new tab), The Quikrete Companies, Undated project sheet.
Manufacturer data.
“Hole depth should be 1/3 the overall post length, plus 6" (150mm) for the gravel base.”
Per QUIKRETE's project sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 1) -
CIP 31, Ordering Ready Mixed Concrete (opens in new tab), National Ready Mixed Concrete Association, 2000, 2016, 2023.
Standards or industry body.
“Quantity of concrete ordered should be 4% to 10% more than an estimate calculated from the plan dimensions to account for contingencies.”
Checked November 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 2) -
QUIKRETE Concrete Mix No. 1101 data sheet (opens in new tab), The Quikrete Companies, Revised October 2022.
Manufacturer data.
“An 80 lb (36.2 kg) bag yields approximately 0.60 ft3 (17 L)”
“A 40 lb (18.1 kg) bag yields approximately 0.30 ft3 (8.5 L)”
“A 50 lb (22.6 kg) bag yields approximately 0.375 ft3 (10.6 L)”
“A 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L)”
“A 90 lb (40.8 kg) bag yields approximately 0.675 ft3 (19.1 L)”
Per QUIKRETE's data sheet, checked Nov 12, 2026. Figures and codes change; verify with the source. Back to where this is used (Source 3)
These are summaries of what the sources say, not professional advice. Codes and product data change. Check with your building department and the product label about your own project.
Sources
- [1] QUIKRETE, QUIKRETE Setting Posts project sheet. Checked November 12, 2026. https://www.quikrete.com/PDFs/Projects/SettingPosts.pdf
- [2] National Ready Mixed Concrete Association, CIP 31, Ordering Ready Mixed Concrete. Checked November 12, 2026. https://www.nrmca.org/wp-content/uploads/2021/01/31pr.pdf
- [3] QUIKRETE, QUIKRETE Concrete Mix No. 1101 data sheet. Checked November 12, 2026. https://www.quikrete.com/PDFs/DATA_SHEET-Concrete%20Mix%201101.pdf