Concrete Column & Post Hole Calculator
Work out concrete for round (Sonotube) or square columns, piers and fence-post holes. Enter a post size and its volume is subtracted from each hole.
Concrete Column & Post Hole Calculator — ConcreteNear.com
| Concrete per column / hole | 3.14 ft³ |
| 80-lb bags per hole | 6 · 5.76 exact |
| Concrete volume (exact) | 0.12 yd³ |
| Cubic feet | 3.1 ft³ |
| 80-lb bags (if mixing by hand) | 6 |
| 60-lb bags | 8 |
| Ready-mix trucks (10 yd³ each) | 1 |
| Approximate weight in place | 0.2 tons |
Cost estimate U.S. average prices
| 80-lb bags (whole bags per hole) 6 bag × $6.50 | $39.00 |
| Estimated total | $39.00 |
| Alternative: Ready-mix concrete 0.25 yd³ × $160.00 | $40.00 |
| Alternative: Short-load fee (last load 0.25 yd³ < 6 yd³) 1 load × $150.00 | $150.00 |
- Under about 1 yd³, bagged mix is usually cheaper than a ready-mix delivery. Compare both below.
- Keep frost footings below your local frost line; flare (bell) the bottom where uplift matters.
| Inputs | |
| Shape | Round (tube or augered hole) |
| Diameter / width | 12 in |
| Height / hole depth | 4 ft |
| Number of columns or holes | 1 |
| Post size set in the concrete (0 = none) | 0 in |
| Extra for waste & over-excavation | 10% |
| Ready-mix truck size | 10 yd³ |
| Short-load minimum | 6 yd³ |
Planning estimate only — confirm with your supplier or contractor.
Prices used — edit any price to match your local quote
| Item | Unit price | Basis & source |
|---|---|---|
| 80-lb bag of concrete mix per bag | starting estimate Starting estimate for a retail shelf price. Check your store. | |
| Ready-mix concrete per yd³ | public source NRMCA Performance Benchmarking Survey — average 2023 U.S. selling price per cubic yard (2023 data) — Plant price before delivery, short-load, wait-time and fuel fees. Concrete Financial Insights reports $179.95/yd³ for 2025 across four public producers (likely higher than small residential pours). | |
| Short-load fee (per truck under the minimum) per load | starting estimate Starting estimate. Ready-mix producers charge a flat or per-yard fee for small loads; ask your dispatcher. |
How to use this calculator
- Pick round or square and enter the hole or tube diameter.
- Enter depth — for fence posts, typically ⅓ to ½ of the post height above ground, below the frost line.
- Enter the post size to subtract it (0 for a solid pier).
- Read bags per hole and the total.
Formulas
Round: ft³ = π × (diameter ÷ 2)² × heightSquare: ft³ = width² × heightNet per hole = hole − post volumeBags = ceiling(ft³ ÷ bag yield) — an 80-lb bag yields about 0.60 ft³
Questions
How many bags of concrete per fence post?
A 10 in hole 3 ft deep with a 4×4 post holds about 1.4 ft³ of concrete — three 80-lb or four 60-lb bags. The calculator does the exact math for your hole.
What size Sonotube do I need?
That comes from your deck or structural plans and the load. 8–12 in tubes are common for decks.
Do I need to mix fast-setting concrete?
Fast-setting mixes are handy for posts; yields per bag are similar but check the bag.
Sources & assumptions
Prices checked 2026-11-10. State pricing multiplies national figures by the U.S. Bureau of Economic Analysis regional price parities (goods for materials, services for labor and services). RPPs compare general consumer price levels (U.S. = 100). They are not construction-specific; we use RPP Goods for materials and RPP Services: Other (excludes rents) for labor and services.
- Ready-mix concrete — NRMCA Performance Benchmarking Survey — average 2023 U.S. selling price per cubic yard (2023 data). Plant price before delivery, short-load, wait-time and fuel fees. Concrete Financial Insights reports $179.95/yd³ for 2025 across four public producers (likely higher than small residential pours).
Starting estimates No public price series was found for: 80-lb bag of concrete mix; Short-load fee (per truck under the minimum). These defaults are editable placeholders — replace them with a local quote.
Results are planning estimates, not quotes or engineering advice. Codes, specifications and your supplier's numbers govern.
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