How Much Concrete for an 8-Inch Round Footing 24 Inches Deep?
Estimate for an 8" diameter × 24" deep round footing — cubic feet, cubic yards, and bag counts
Exact volume and bag counts for an 8" diameter by 24" deep round footing. Shows cubic feet, cubic yards, and planning quantities with a 10% waste allowance.
This is an 8" diameter × 24" deep round footing poured in a tube form. It's a narrow, small-volume cylinder — the sort you make for isolated post supports or a tight column layout.
Expect shallow excavation and a small concrete order. Plan bags or a minimal ready-mix delivery and keep an eye on load, soil bearing capacity, frost depth, and whether reinforcement is needed for your column or post application.
Quick Answer
Exact volume: 0.6981 cubic feet (0.0259 cubic yards).
Planning with 10% waste: 0.7679 cubic feet (0.0285 cubic yards). Planning bag counts: 3 40-lb bags, 2 60-lb bags, or 2 80-lb bags (these are the waste-adjusted counts).
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How to Use This Footing Estimate
Quick steps to estimate and order for this 8" × 24" round footing:
- Confirm diameter (8") and depth (24") at the pour location.
- Use the listed volume per footing (0.6981 cu ft) to check totals.
- Add a waste allowance — this page uses 10% (0.7679 cu ft planning volume).
- Decide bagged concrete or ready-mix based on how many footings you have.
- If pouring multiple footings, multiply the planning volume and bag counts before ordering.
- Round bag counts up to whole bags and keep a couple extras on site.
Formula
Use this round footing formula:
Volume (ft³) = π × Radius (ft) × Radius (ft) × Depth (ft)
3.1416 × 0.33 × 0.33 × 2 = 0.7 ft³
0.7 ÷ 27 = 0.03 yd³
If you add a 10% waste allowance, you should plan closer to 0.03 cubic yards.
Worked Example
Single footing example — before waste: 0.6981 cu ft (0.0259 yd³). With 10% waste: 0.7679 cu ft (0.0285 yd³). Bag counts: exact counts are 3 40-lb, 2 60-lb, or 2 80-lb; the planning counts with waste are the same numbers rounded.
Multiple-footing example (4 footings) — total before waste: 2.7924 cu ft (0.1036 yd³). With 10% waste: 3.0716 cu ft (0.1140 yd³). Planning bags: 12 40-lb bags, 8 60-lb bags, or 8 80-lb bags.
Bag Count Estimate
- 2 bags of 80 lb concrete mix
- 2 bags of 60 lb concrete mix
- 3 bags of 40 lb concrete mix
Always verify the actual yield on the product label before buying materials.
When Bagged Concrete vs Ready-Mix Makes Sense
For a single 8" × 24" footing, bagged concrete is usually simpler. This pour is under one cubic foot, so mixing a few bags on site avoids a truck mix charge and long wait times.
If you have several footings — for example, a dozen — ready-mix becomes more attractive because it saves mixing time and gives consistent placement. For small counts, stick with bags; for higher counts, compare the total bag count to a minimal ready-mix delivery.
Common Uses for This Footing Size
This 8" diameter by 24" deep footing often fits isolated post supports: pergola posts, deck posts, fence columns, sign posts, or other narrow-column layouts where the footprint must stay small. The tube-form shape makes it straightforward to place under a single column or in a close-knit pattern of small footings.
Its suitability depends on the load, soil bearing capacity, frost depth in your area, and whether the footing needs reinforcement. In heavier load or poor-soil situations, a larger diameter, deeper footing, or added rebar might be required.
Common Mistakes to Avoid
Common estimating and planning oversights:
- Not using the cylinder formula and miscalculating volume.
- Failing to add a waste allowance — small pours still need extra material.
- Confusing exact bag counts with waste-adjusted planning counts.
- Ordering only whole bags without rounding up enough for spillage.
- Ignoring reinforcement needs for the post or column being supported.
- Forgetting to multiply volumes correctly when ordering for multiple footings.
Frequently Asked Questions
What is the exact concrete volume for an 8" diameter × 24" deep round footing?
The exact volume is 0.6981 cubic feet, which is 0.0259 cubic yards.
How many bags of concrete mix do I need for one footing?
Exact bag counts are 3 40-lb bags, 2 60-lb bags, or 2 80-lb bags for one footing.
Why include a 10% waste allowance and how does it change the quantity?
A 10% waste allowance covers spillage and small overages; it raises the footing volume to 0.7679 cu ft (0.0285 yd³) and is the basis for the planning bag counts shown.
Will this footing size work for a deck post or pergola column?
An 8" × 24" round footing is sometimes used for deck or pergola posts, but adequacy depends on the post load, soil bearing capacity, frost depth, and reinforcement. Check those factors before relying on this size.
Keep Planning Your Concrete Project
Use the calculator, compare more footing pages, and review your estimate before buying materials.
Disclaimer: This page provides planning estimates only. Actual concrete needs vary with excavation accuracy, site conditions, local code requirements, bag yield, and supplier guidance. Always verify measurements before buying materials, and consult a qualified professional for structural or code-sensitive work.