How Much Concrete for a 36-Inch Round Footing 36 Inches Deep?
Estimate 21.2058 cu ft (0.7854 yd³) and bag counts for a 36" diameter × 36" deep round footing.
Concrete volume and bag planning for a 36" round Sonotube footing, 36" deep. Exact volume 21.2058 cu ft (0.7854 yd³) plus 10% waste planning totals and bag counts.
Bags of concrete for a 36" diameter × 36" deep round footing add up quickly. This page lists the exact volume, the 10% waste-adjusted volume, and the bag counts for one tube-form footing at this size.
The pour is a narrow cylindrical footing 36" across and 36" deep. It’s often used for isolated post supports or narrow layouts; confirm reinforcement and permit requirements if the supported load or frost depth is significant.
Quick Answer
Exact volume: 21.2058 cubic feet (0.7854 cubic yards) for one 36" diameter × 36" deep round footing.
Planning with 10% waste: 23.3264 cubic feet (0.8639 cubic yards). Planning bag counts: 78 40-lb bags, 52 60-lb bags, or 39 80-lb bags (planning counts are waste-adjusted; exact counts below).
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 for this round footing size.
- Confirm the tube outside diameter is 36" and depth is 36"—use those dimensions for the volume math.
- Use the cylinder formula to check the exact volume (21.2058 cu ft). Keep that number for ordering bulk mix or comparing bag totals.
- Add a waste allowance (this page uses 10%) to get 23.3264 cu ft for purchase planning.
- Decide material: bags of concrete mix for a single footing, ready-mix for several footings or when working time and consistency matter.
- If ordering multiple footings, multiply the planning volume and round bag counts up to whole bags before you buy.
- Buy an extra bag or two beyond the planning number on the day of work to cover small shortfalls.
Formula
Use this round footing formula:
Volume (ft³) = π × Radius (ft) × Radius (ft) × Depth (ft)
3.1416 × 1.5 × 1.5 × 3 = 21.21 ft³
21.21 ÷ 27 = 0.79 yd³
If you add a 10% waste allowance, you should plan closer to 0.86 cubic yards.
Worked Example
Single-footing example (one tube): before waste the footing needs 21.2058 cu ft (0.7854 yd³). Exact bag counts for one footing are 71 40-lb bags, 48 60-lb bags, or 36 80-lb bags. With 10% waste that becomes 23.3264 cu ft (0.8639 yd³) and planning bag counts of 78 40-lb, 52 60-lb, or 39 80-lb.
Multiple-footing example (four tubes): total before waste = 84.8232 cu ft (3.1416 yd³). With 10% waste the total = 93.3056 cu ft (3.4556 yd³). Planning bag totals for four footings: 312 40-lb bags, 208 60-lb bags, or 156 80-lb bags.
Bag Count Estimate
- 39 bags of 80 lb concrete mix
- 52 bags of 60 lb concrete mix
- 78 bags of 40 lb concrete mix
Always verify the actual yield on the product label before buying materials.
Bag Counts by Waste Buffer for 36" 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 | 21.21 | 36 | 48 | 71 |
| +5% typical DIY | 22.27 | 38 | 50 | 75 |
| +10% recommended | 23.33 | 39 | 52 | 78 |
| +15% rough conditions | 24.39 | 41 | 55 | 82 |
When Bagged Concrete vs Ready-Mix Makes Sense
For a single 36" × 36" footing, bagged concrete is often simpler: you can mix what you need on site and avoid a truck minimum. One footing is 71 40-lb bags exactly, or 78 when you include 10% waste planning.
Ready-mix becomes more sensible when pouring several footings in one day. Once you hit multiple tubes (three or four), the labor and consistency advantages of a small ready-mix delivery often outweigh hauling and mixing dozens of bags.
Common Uses for This Footing Size
This 36" diameter × 36" deep round footing is commonly used for isolated post supports that need a narrow footprint—examples include pergola posts, deck or porch posts, signposts, and other cylindrical footing layouts where space is limited.
Limits depend on the load, soil bearing capacity, frost depth, and reinforcement. Heavy loads, poor bearing soil, or deep frost lines can require larger footings or engineered detail. Confirm permit and code requirements with the local building department and get a structural review if loads are significant.
Common Mistakes to Avoid
Common estimating and ordering mistakes for this footing size.
- Using the tube outside diameter incorrectly instead of the required pour diameter when you calculate volume.
- Confusing exact bag counts with waste-adjusted planning counts and ordering the smaller number by mistake.
- Rounding down bag totals instead of up, leaving you short on the day.
- Forgetting to multiply both the exact volume and the waste-adjusted volume when ordering several footings.
- Assuming bag counts convert linearly without accounting for small differences in mix yield between brands.
- Ordering ready-mix for a single tube without comparing bag cost and the supplier’s minimum truck charge.
Frequently Asked Questions
What is the exact concrete volume for a 36" diameter by 36" deep round footing?
The exact volume is 21.2058 cubic feet, which equals 0.7854 cubic yards for one 36" × 36" round footing.
How many bags of concrete do I need for this footing?
Exact counts are 71 40-lb bags, 48 60-lb bags, or 36 80-lb bags for one footing. Planning counts with 10% waste are 78, 52, or 39 respectively.
Why include a 10% waste allowance and how does it affect ordering?
Ten percent covers spill, over-excavation, and mixing losses. It raises the purchase volume from 21.2058 cu ft to 23.3264 cu ft and increases bag planning counts to 78 40-lb bags (or equivalents).
Is this footing size adequate for a deck post or pergola column?
A 36" × 36" round footing is often used for isolated post supports, but adequacy depends on the column load, soil bearing capacity, frost depth, and reinforcement. Have a structural review if loads are heavy or site conditions are uncertain.
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.