How Much Concrete for a 30-Inch Round Footing 36 Inches Deep?
Material and volume numbers for a 30" diameter × 36" deep round footing — cubic feet, cubic yards, and bag counts
Exact and planning estimates for a 30" round Sonotube footing 36" deep: 14.7262 cu ft (0.5454 yd3) exact, plus bag counts and a 10% waste planning total.
Start with the material. A 30" diameter × 36" deep round form is a narrow, tube-style footing that only needs about 14.7262 cubic feet of concrete for the actual pour. If you prefer thinking in bags, that exact volume equals 50 40-lb bags, 33 60-lb bags, or 25 80-lb bags.
This footprint is useful for isolated, cylindrical supports where a narrow column layout is used. The excavation depth is 36"; depending on reinforcement and load you may need different sizing, so treat these numbers as planning estimates rather than a full structural design.
Quick Answer
Exact volume: 14.7262 cubic feet (0.5454 cubic yards). Exact bag counts for the poured volume: 50 40-lb bags, 33 60-lb bags, or 25 80-lb bags.
Planning with 10% waste: 16.1988 cubic feet (0.5999 cubic yards). Order planning quantities: 54 40-lb bags, 36 60-lb bags, or 27 80-lb bags to include a 10% allowance.
Need a custom estimate? Use the Footing Calculator. Browse footing size pages. All project pages.
How to Use This Footing Estimate
A quick sequence to move from estimate to purchase for a single 30" × 36" round footing.
- Confirm diameter is 30" and depth is 36" — those are the numbers used here.
- Check the exact volume: 14.7262 cu ft (0.5454 yd3). Use that for precise ordering when possible.
- Add a 10% allowance for waste and spillage — planning volume is 16.1988 cu ft (0.5999 yd3).
- Decide material: bags of concrete mix for single pours, ready-mix for multiple pours or larger totals.
- Scale quantities if pouring more than one footing — multiply the per-footing planning numbers before ordering.
- Round bag counts to whole bags and confirm transport or mixing method before purchase.
Formula
Use this round footing formula:
Volume (ft³) = π × Radius (ft) × Radius (ft) × Depth (ft)
3.1416 × 1.25 × 1.25 × 3 = 14.73 ft³
14.73 ÷ 27 = 0.55 yd³
If you add a 10% waste allowance, you should plan closer to 0.6 cubic yards.
Worked Example
Single-footing example: before waste the footing needs 14.7262 cu ft (0.5454 yd3). With a 10% waste allowance plan on 16.1988 cu ft (0.5999 yd3) and order 54 40-lb bags, 36 60-lb bags, or 27 80-lb bags.
Four-footing example: before waste total = 58.9048 cu ft (2.1816 yd3). With 10% waste total = 64.7952 cu ft (2.3996 yd3). Order totals: 216 40-lb bags, 144 60-lb bags, or 108 80-lb bags for the four-footing job.
Bag Count Estimate
- 27 bags of 80 lb concrete mix
- 36 bags of 60 lb concrete mix
- 54 bags of 40 lb concrete mix
Always verify the actual yield on the product label before buying materials.
Bag Counts by Waste Buffer for 30" 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 | 14.73 | 25 | 33 | 50 |
| +5% typical DIY | 15.46 | 26 | 35 | 52 |
| +10% recommended | 16.2 | 27 | 36 | 54 |
| +15% rough conditions | 16.94 | 29 | 38 | 57 |
When Bagged Concrete vs Ready-Mix Makes Sense
For this single 30" × 36" footing, bagged concrete is often the simplest option. One person or a small crew can handle mixing several dozen 40-lb bags, and you avoid a short ready-mix truck minimum for a small 0.5454 yd3 pour.
When you have multiple footings — for example, four or more — the total volume rises into multiple cubic yards and a ready-mix truck becomes more practical. Ready-mix reduces on-site mixing time and gives a single continuous pour, but for one footing the bag route usually keeps logistics and waste simpler.
Common Uses for This Footing Size
This 30" diameter by 36" deep round footing is often used for isolated post supports in narrow layouts: pergola posts, deck posts on individual pads, sign posts, or single-column supports where a cylindrical footing footprint fits the design. The narrow tube form keeps the poured volume relatively small while providing a dedicated bearing area.
Limits and conditions matter: adequacy depends on the applied load, soil bearing capacity, frost depth, and whether reinforcement like rebar or anchors is required. For heavier columns, weak soils, or deep frost zones, larger diameters, deeper footings, or engineered details may be needed.
Common Mistakes to Avoid
Common estimating and ordering mistakes to avoid for a 30" × 36" round footing:
- Using diameter instead of radius in the formula when calculating volume.
- Ordering only the exact volume and forgetting a 10% waste allowance.
- Mixing different bag sizes mentally and then miscounting total bags needed.
- Failing to multiply planning numbers correctly when ordering for multiple footings.
- Assuming bagged mixing speed without accounting for time and help required.
- Not confirming reinforcement or anchor placement before pouring, which can force rework.
Frequently Asked Questions
What is the exact concrete volume for a 30" round footing 36" deep?
The exact volume is 14.7262 cubic feet, which is about 0.5454 cubic yards.
How many bags of concrete do I need for this footing?
Exact poured volume uses 50 40-lb bags, 33 60-lb bags, or 25 80-lb bags. With a 10% waste allowance plan on 54 40-lb, 36 60-lb, or 27 80-lb bags.
Why include a 10% waste allowance and how was it applied here?
A 10% allowance covers spillage, over-excavation, and slight measurement errors. The single-footing planning volume is 16.1988 cu ft (0.5999 yd3), which is 10% above the exact 14.7262 cu ft.
Will this footing size work for my deck or pergola post?
It may work in some cases for deck or pergola posts, but adequacy depends on the post load, soil bearing, frost depth, and required reinforcement. Use these volume numbers for material planning and get a structural check if loads or conditions are uncertain.
Keep Planning Your Concrete Project
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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.