How Much Concrete for a 24-Inch Round Footing 36 Inches Deep?
Estimate for a 24" diameter × 36" deep round footing — cubic feet, cubic yards, and bag counts
Quick planning numbers for a 24" round Sonotube footing 36" deep: exact volume, waste-adjusted volume, and bag counts for 40/60/80 lb mixes.
24" diameter × 36" deep is a narrow, small-volume round pour formed with a tube. This page gives the concrete math for that exact cylinder-sized footing so you can plan materials without guessing.
It’s commonly used for isolated post supports and similar small residential loads. Keep in mind excavation depth, reinforcement choice, and frost depth can affect whether this diameter and depth are right for the load.
Quick Answer
Exact volume: 9.4248 cubic feet (0.3491 cubic yards) for one 24" diameter × 36" deep round footing.
Planning with 10% waste: 10.3673 cubic feet (0.384 cubic yards). Plan on 35 40-lb bags, 24 60-lb bags, or 18 80-lb bags to include the 10% allowance.
Need a custom estimate? Use the Footing Calculator. Browse footing size pages. All project pages.
How to Use This Footing Estimate
Fast steps to estimate and prepare material for this 24" × 36" round footing.
- Measure the tube diameter and depth to confirm 24" diameter × 36" deep.
- Confirm the exact volume (9.4248 cu ft) and add a 10% waste allowance.
- Decide bagged mix or ready-mix based on number of footings.
- If pouring multiple footings, multiply the planning volume and bag counts by the number of footings.
- Round up bag counts to whole bags and order a little extra for spillage and variations.
- Schedule delivery or buy bags shortly before the pour so bags stay dry and usable.
Formula
Use this round footing formula:
Volume (ft³) = π × Radius (ft) × Radius (ft) × Depth (ft)
3.1416 × 1 × 1 × 3 = 9.42 ft³
9.42 ÷ 27 = 0.35 yd³
If you add a 10% waste allowance, you should plan closer to 0.38 cubic yards.
Worked Example
Single footing: before waste the footing is 9.4248 cu ft (0.3491 yd³). With a 10% allowance the planning volume is 10.3673 cu ft (0.384 yd³) and that corresponds to 35 40-lb bags, 24 60-lb bags, or 18 80-lb bags.
Multiple footings: four identical footings total 37.6992 cu ft (1.3964 yd³) before waste. With 10% waste the total is 41.4692 cu ft (1.536 yd³). For four footings order about 140 40-lb bags, 96 60-lb bags, or 72 80-lb bags.
Bag Count Estimate
- 18 bags of 80 lb concrete mix
- 24 bags of 60 lb concrete mix
- 35 bags of 40 lb concrete mix
Always verify the actual yield on the product label before buying materials.
Bag Counts by Waste Buffer for 24" diameter × 36" 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 | 9.42 | 16 | 21 | 32 |
| +5% typical DIY | 9.9 | 17 | 22 | 33 |
| +10% recommended | 10.37 | 18 | 24 | 35 |
| +15% rough conditions | 10.84 | 19 | 25 | 37 |
When Bagged Concrete vs Ready-Mix Makes Sense
For a single 24" × 36" footing, bagged concrete is often simpler: you can buy the 35 40-lb bags (or the equivalent 24 of 60-lb or 18 of 80-lb) and mix on site. It avoids ordering a truck for less than half a cubic yard of concrete.
If you have several of these footings the totals add up quickly. Once you’re near 1 cubic yard or more (for example several footings), a small ready-mix delivery becomes faster and reduces site mixing time.
Common Uses for This Footing Size
This 24" diameter by 36" deep footing is sized for isolated post supports and narrow cylindrical footing layouts — think pergola posts, deck posts, sign posts, and small porch columns where a slim footprint is preferred.
Its actual adequacy depends on applied load, soil bearing capacity, frost depth, reinforcement choice, and any permit or inspection requirements. Those factors will determine whether this diameter and depth are appropriate for your specific support.
Common Mistakes to Avoid
Common estimating and planning mistakes to avoid for this footing size.
- Using the tube outer diameter instead of the finished formed diameter when calculating volume.
- Forgetting the 10% waste allowance and ordering exactly 9.4248 cu ft worth of material.
- Miscalculating bag conversions (mixing exact vs planning bag counts).
- Ordering too few bags because you rounded down instead of up.
- Assuming rebar or post sleeve displacement will significantly reduce needed concrete without measuring it.
- Not factoring multiple footings into a single order — small orders can multiply quickly.
Frequently Asked Questions
What is the exact concrete volume for a 24" diameter × 36" deep footing?
The exact volume is 9.4248 cubic feet, which equals 0.3491 cubic yards for one footing.
How many bags of concrete mix do I need for this footing?
Exact bag counts for one footing are 32 40-lb bags, 21 60-lb bags, or 16 80-lb bags. With a 10% planning allowance order 35 40-lb, 24 60-lb, or 18 80-lb bags.
Why add a 10% waste allowance and how much does that change the volume?
A 10% waste allowance covers spillage and mixing differences. It raises the volume from 9.4248 cu ft to 10.3673 cu ft (0.3491 yd³ to 0.384 yd³) for one footing.
Is this footing size suitable for a deck post or pergola column?
A 24" × 36" footing is sometimes used for isolated deck or pergola posts and similar supports, but adequacy depends on the post load, soil bearing, frost depth, and whether reinforcement is required.
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.