How Much Concrete for a 20-Inch Round Footing 24 Inches Deep?
Estimate for a 20" diameter × 24" deep round footing — cubic feet, cubic yards, and bag counts
Exact and planning quantities for a 20" round Sonotube footing 24" deep: volume in cu ft and yd3, exact bag counts, and waste-adjusted planning counts for ordering.
This is a small-volume round pour using a 20" diameter Sonotube form at 24" deep. The tube shape keeps the footprint narrow and the pour is straightforward to estimate.
Expect about 4.36 cubic feet of concrete per footing. That usually works out to the bag counts shown below for a single pour; deeper excavation, embedment, reinforcement, or heavier loads will change requirements.
Quick Answer
Exact volume: 4.3633 cubic feet (0.1616 cubic yards).
Planning with 10% waste: 4.7996 cu ft (0.1778 yd³). Plan on 16 40-lb bags, 11 60-lb bags, or 8 80-lb bags for the waste-adjusted single-footing order.
Need a custom estimate? Use the Footing Calculator. Browse footing size pages. All project pages.
How to Use This Footing Estimate
Quick steps to estimate and order concrete for this round footing.
- Measure the tube: 20" diameter and 24" deep (radius 0.8333 ft, depth 2 ft).
- Compare the calculated volume (4.3633 cu ft) to product yields on bag labels.
- Add a waste allowance — this page uses 10% (4.7996 cu ft planning volume).
- Decide bagged mix vs ready-mix based on total yards and number of footings.
- If ordering multiple footings, multiply the exact volume and then apply the waste allowance to the total.
- Round bag counts up to whole bags and confirm delivery timing for ready-mix if used.
Formula
Use this round footing formula:
Volume (ft³) = π × Radius (ft) × Radius (ft) × Depth (ft)
3.1416 × 0.83 × 0.83 × 2 = 4.36 ft³
4.36 ÷ 27 = 0.16 yd³
If you add a 10% waste allowance, you should plan closer to 0.18 cubic yards.
Worked Example
Single-footing example: the exact volume is 4.3633 cu ft (0.1616 yd³) before waste. With a 10% allowance the planning volume is 4.7996 cu ft (0.1778 yd³).
Multiple-footing example (3 footings): exact total = 13.0899 cu ft (0.4848 yd³). With 10% waste the planning total uses the per-footing planning bags: 48 40-lb bags, 33 60-lb bags, or 24 80-lb bags for the three-footing order.
Bag Count Estimate
- 8 bags of 80 lb concrete mix
- 11 bags of 60 lb concrete mix
- 16 bags of 40 lb concrete mix
Always verify the actual yield on the product label before buying materials.
Bag Counts by Waste Buffer for 20" diameter × 24" deep
Pick a buffer based on site conditions: clean forms and accurate measurements can run leaner; rough subgrade or hard-to-reach pours need more cushion.
| Buffer | Volume (ft³) | 80 lb bags | 60 lb bags | 40 lb bags |
|---|---|---|---|---|
| No buffer | 4.36 | 8 | 10 | 15 |
| +5% typical DIY | 4.58 | 8 | 11 | 16 |
| +10% recommended | 4.8 | 8 | 11 | 16 |
| +15% rough conditions | 5.02 | 9 | 12 | 17 |
When Bagged Concrete vs Ready-Mix Makes Sense
For a single 20" × 24" footing, bagged concrete is often simpler. One person can mix a few 40- or 60-lb bags at a time and pour a narrow tube without waiting for a truck. The planning counts here show 16 40-lb bags (with waste) for one footing.
If you have several footings and the total yardage climbs (several tenths of a cubic yard or more), a short ready-mix delivery can reduce mixing time and improve consistency. For just one or two of these 20" footings, bags usually remain the more convenient option.
Common Uses for This Footing Size
This 20" diameter by 24" deep footing is sized for narrow, isolated supports — think single post or column locations where a small round footing fits the layout. It often appears under pergola posts, deck posts, sign posts, or other situations that use cylindrical footings and require a compact footprint.
Actual suitability depends on the applied load, soil bearing capacity, frost depth in your area, and whether steel reinforcement is required. Keep those factors in mind and be ready to adjust diameter, depth, or reinforcement if the load or site conditions demand it; local permits or inspections may also affect final sizing.
Common Mistakes to Avoid
Common estimating and ordering mistakes to avoid:
- Using the diameter instead of the radius when calculating volume.
- Forgetting to include a waste allowance — small pours are still subject to spillage and shortfalls.
- Ordering exact bag counts without rounding up to whole bags.
- Failing to multiply bag counts correctly when ordering multiple footings.
- Assuming reinforcement or deeper embedment without adjusting volume and bag totals.
- Not confirming delivery timing for ready-mix when ordering multiple footings.
Frequently Asked Questions
What is the exact concrete volume for a 20" diameter × 24" deep footing?
The exact calculated volume is 4.3633 cubic feet, which equals 0.1616 cubic yards.
How many bags of concrete do I need for one footing?
Exact single-footing bag counts are 15 40-lb bags, 10 60-lb bags, or 8 80-lb bags; with a 10% waste allowance plan on 16 40-lb, 11 60-lb, or 8 80-lb bags.
Why include a 10% waste allowance and how is it applied?
A 10% allowance covers small spills, over-excavation, and finish adjustments; the planning volume becomes 4.7996 cu ft (0.1778 yd³) for a single footing and you use the waste-adjusted bag counts for ordering.
Is this footing size adequate for a deck post or pergola column?
It may work in some cases for a deck post or pergola column, but adequacy depends on the applied load, soil bearing, frost depth, and reinforcement. Confirm 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.