How Much Concrete for a 16-Inch Round Footing 36 Inches Deep?
Estimate for a 16" diameter × 36" deep round footing: cubic feet, cubic yards, and bag counts
Exact volume and bag counts for a 16-inch round Sonotube footing 36 inches deep. See cubic feet, cubic yards, exact bags, and a 10% planning allowance.
This is a narrow, tube-form footing: 16" diameter × 36" deep. It’s a small-volume round pour that’s easy to plan before you break ground.
Use this page when you need the exact quantities for one 16-inch round footing 36" deep. Keep in mind soil bearing, applied load, and reinforcement choices affect actual design and sizing.
Quick Answer
Exact volume: 4.1888 cubic feet (0.1551 cubic yards). Exact bag counts for a single pour: 14 40-lb bags, 10 60-lb bags, or 7 80-lb bags.
Planning (10% waste): 4.6077 cubic feet (0.1706 cubic yards). Plan on 16 40-lb bags, 11 60-lb bags, or 8 80-lb bags for ordering and rounding up.
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 plan this 16" × 36" round footing.
- Measure the footing diameter and depth to confirm 16" by 36" (inside tube dimension).
- Confirm the exact volume: 4.1888 cu ft (0.1551 yd³) for one footing.
- Add a waste allowance — we use 10% here — giving 4.6077 cu ft for ordering.
- Choose material: bagged concrete for one or a few footings, ready-mix when ordering many.
- If you have multiple footings, multiply the planning volume and bags, then round up when you buy.
- Order one size larger in bags if you want a small margin beyond the 10% allowance.
Formula
Use this round footing formula:
Volume (ft³) = π × Radius (ft) × Radius (ft) × Depth (ft)
3.1416 × 0.67 × 0.67 × 3 = 4.19 ft³
4.19 ÷ 27 = 0.16 yd³
If you add a 10% waste allowance, you should plan closer to 0.17 cubic yards.
Worked Example
Single-footing example — before waste: 4.1888 cu ft (0.1551 yd³). With 10% waste: 4.6077 cu ft (0.1706 yd³). Bags: exact = 14 40-lb, 10 60-lb, 7 80-lb; planning = 16 40-lb, 11 60-lb, 8 80-lb.
Multiple-footing example (4 footings) — before waste: 16.7552 cu ft (0.6206 yd³). With 10% waste: 18.4307 cu ft (0.6827 yd³). Bags (planning): 64 40-lb, 44 60-lb, 32 80-lb.
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.
When Bagged Concrete vs Ready-Mix Makes Sense
For a single 16" × 36" footing, bagged concrete is usually simpler. You can mix a small batch and use about 16 40-lb bags after the 10% allowance, which is easy to handle on most jobsites.
If you have several footings (four or more) the labor and consistency needs often push toward ready-mix. Ready-mix becomes more efficient when small batches would take long to mix and place, or when you need consistent slump for several pours.
Common Uses for This Footing Size
This 16" diameter × 36" deep footing often works for isolated post supports and narrow cylindrical layouts where space is limited. Examples include pergola posts, typical deck posts on a narrow grid, sign supports, and similar uses where a narrow footprint is required.
Limits come down to applied load, soil bearing capacity, frost depth, and whether you need reinforcement. This size is sometimes used for moderate loads, but final adequacy depends on those factors and any permit or plan requirements for your project.
Common Mistakes to Avoid
Common estimating and ordering mistakes for a 16" round, 36" deep footing.
- Using the tube outside diameter instead of the internal pouring diameter and under-ordering concrete.
- Forgetting the 10% waste and arriving short during the pour.
- Rounding bag counts down instead of up when converting volumes to bags.
- Mixing by eye and producing inconsistent batches for multiple footings.
- Not multiplying the single-footing volume correctly when ordering for several footings.
- Assuming bag weights scale linearly without accounting for yield differences between mix brands.
Frequently Asked Questions
What is the exact concrete volume for one 16-inch round footing 36 inches deep?
One 16" diameter × 36" deep footing requires 4.1888 cubic feet of concrete, which is 0.1551 cubic yards.
How many bags of concrete do I need for this footing?
Exact counts: 14 40-lb bags, 10 60-lb bags, or 7 80-lb bags. With a 10% planning allowance use 16 40-lb, 11 60-lb, or 8 80-lb.
Why include a 10% waste allowance and how does it change the order?
The 10% allowance covers minor spillage, grooves, and measurement rounding. It raises the volume to 4.6077 cu ft (0.1706 yd³) for ordering and increases bag counts accordingly.
Is this footing size adequate for a deck or pergola post?
A 16" × 36" footing is sometimes used for deck or pergola posts, but adequacy depends on the actual load, soil bearing, frost depth, and reinforcement requirements. Review those factors before finalizing 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.