Calculated result
1yd³
Ready-mix order
Formula
CONC-POSTHOLE-001π ÷ 4 × (hole diameter² − post diameter²) × depth × count × (1 + waste)
20.94 ft³
Net concrete volume
0.78 yd³
Net volume
52 bags
Bags to order
Concrete calculator
Post hole calculator
Concrete volume and bag count for round fence or deck post holes, including solid sonotube piers when post diameter is zero.
By Feroz Sheikh · Formula CONC-POSTHOLE-001 v1.1.0 · Tested formula
Formula
CONC-POSTHOLE-001v1.1.0Project inputs
Enter your measurements. Switching units converts the same project, including coverage and unit rates. Package yields keep the unit printed beside each field.
Refine measurements and rates at any time. Your current values are included in the material-list PDF.
Planning estimate, not engineering advice. Confirm site measurements and product specifications. Calculation limits.
This calculator returns concrete volume and bags for round fence or deck piers. Formula CONC-POSTHOLE-001 v1.1.0. Set post diameter to zero for a solid sonotube. Add the bags to an estimate. It does not set frost depth or a footing size.
- Measure hole or tube diameter and the actual post diameter, or enter 0 to fill the hole solid.
- Enter identical-hole count and concrete depth, not the frost-line rule of thumb alone.
- Replace bag yield with the selected mix label before treating bags as an order.
Size chart
Post hole chart (12 in hole, 4 in post, 36 in deep, 10% waste)
Set post diameter to zero for a solid sonotube. Not a frost-depth spec.
| Holes | Primary | Check |
|---|---|---|
| 4 holes | 0.5 yd³ | 8.38 ft³ |
| 6 holes | 0.75 yd³ | 12.57 ft³ |
| 8 holes | 0.75 yd³ | 16.76 ft³ |
| 10 holes | 1 yd³ | 20.94 ft³ |
Metric example — 10 holes. Ten 12 in holes, 4 in posts, 36 in deep with 10% waste return 0.7 m³.
- Volume method. Length × width × depth, or cylinder volume for holes. Ready-mix is still ordered by volume. Concrete Network — volume calculation guidance
- Bag yield. Use the yield printed on the sack. Bags belong on small pads and post holes. Sakrete — estimating bagged concrete jobs
Add your project costs
Enter supplier prices and any labour, equipment or delivery costs. Pick a currency — badges, inputs, and totals follow.
Enter your supplier’s ready-mix concrete rate in the selected unit. Add delivery, pumping, short-load fees and placing labour as separate project costs. For GCC projects, select QAR, AED, SAR, KWD, OMR or BHD and enter local supplier rates.
How this calculator works
A transparent post hole calculator takeoff.
Feroz SheikhWritten by Feroz Sheikh · founder
This calculator treats each post hole as a round cylinder and subtracts the post when a diameter is entered, then applies a visible allowance before ready-mix rounding and bag count.
Post holes are cylinders: diameter × depth × count, then bags. A fence post in sand is not a deck post in clay — hole volume changes, the bag yield stays labelled.
Worked example. Example: ten 12 in holes, 36 in deep, around 4 in posts contain about 20.94 ft³ of concrete. With 10% allowance the ready-mix order rounds to 1.00 yd³ and 52 bags at 0.45 ft³ each.
See the example inputs and calculated result
This separate example uses the calculator's starting values in imperial units. It stays unchanged when you edit the tool above. Example rates, yields and dimensions are assumptions, not recommendations for your project.
| Input | Example value |
|---|---|
| Hole or tube diameter | 12 in |
| Post diameter | 4 in |
| Hole depth | 36 in |
| Number of holes | 10 count |
| Bag yield | 0.45 ft³ / bag |
| Waste factor | 10 % |
Example result: Ready-mix order — 1 yd³.
π ÷ 4 × (hole diameter² − post diameter²) × depth × count × (1 + waste)
Use the labelled units above when reproducing this example. To work in metric, switch the calculator to Metric; applicable measurements are converted, while product-specific units remain labelled.
- 1. Measure hole or tube diameter and the actual post diameter, or enter 0 to fill the hole solid.
- 2. Enter identical-hole count and concrete depth, not the frost-line rule of thumb alone.
- 3. Replace bag yield with the selected mix label before treating bags as an order.
Field notes that change the number
- Diameter is the hole, not the post.
- Bell-shaped bottoms are extra volume.
- Use the bag calculator when the pour is a handful of piers; a long fence is still a bag job, a pile of garage piers may not be.
Common mistakes
- Using post size as hole size.
- Skipping waste because “it is only holes.”
- Calling this a frost-depth design.
Need the broader workflow? Read the concrete planning guide.
How-to: Concrete for solid tube forms: diameter, height and tube count · Ready-mix or bags: when each makes sense · How to plan a wood fence · How to fill fence and deck post holes
Questions
Questions about post hole calculator
Is this a sonotube calculator?
Enter 0 for post diameter to fill a cardboard tube or hole solid. That is a planning fill quantity, not a pier design.
Does this set hole depth or diameter?
No. Frost line, soil, post size and local requirements must be confirmed independently. This tool only estimates concrete quantity.
How much concrete for 10 post holes?
Ten 12 in holes, 4 in posts, 36 in deep with 10% waste return 1 yd³. Set post diameter to zero for a solid sonotube.
Bags or a truck for fence posts?
Bags for a handful of holes. A truck once the volume climbs past about a yard.
What is the formula ID?
This post hole calculator publishes formula CONC-POSTHOLE-001, version 1.1.0. The ID stays on the result and on the estimate line.