How Much Concrete for a 36-Inch Round Footing 48 Inches Deep?
Planning numbers for a 36" diameter × 48" deep round footing: cubic feet, cubic yards, and bag counts
Exact and waste-adjusted concrete for a 36" round Sonotube footing, 48" deep: volumes in cubic feet and yards plus bag counts for 40 lb, 60 lb, and 80 lb mixes.
This is a planning page for a 36" diameter × 48" deep round footing formed in a tube-style form. The pour is a narrow cylinder—about 28.2743 cubic feet of concrete before waste.
Expect to work with a 48" deep excavation and a long, narrow pour. Bagged concrete is straightforward for this single tube; if you plan multiple footings, scale the numbers and talk with your building department about reinforcement and any permit requirements.
Quick Answer
Exact volume: 28.2743 cubic feet (1.0472 cubic yards).
Planning with 10% waste: 31.1017 cubic feet (1.1519 cubic yards). Exact bag counts are 95 40-lb bags, 63 60-lb bags, or 48 80-lb bags. With waste plan on 104 40-lb bags, 70 60-lb bags, or 52 80-lb bags.
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How to Use This Footing Estimate
Quick steps to move from estimate to purchase for this 36" × 48" round footing.
- Confirm footing diameter and depth on site: 36" diameter, 48" deep.
- Use the cylinder volume above to check your numbers: 28.2743 cu ft before waste.
- Add a waste allowance (we use 10%) to get 31.1017 cu ft for ordering.
- Decide material: bags of concrete mix for a single tube, or ready-mix if several tubes add up to larger yards.
- Convert to bag counts or yards and round up to whole bags or truckloads.
- For multiple footings, multiply the planning volume by the number of footings and then round up before you order.
Formula
Use this round footing formula:
Volume (ft³) = π × Radius (ft) × Radius (ft) × Depth (ft)
3.1416 × 1.5 × 1.5 × 4 = 28.27 ft³
28.27 ÷ 27 = 1.05 yd³
If you add a 10% waste allowance, you should plan closer to 1.15 cubic yards.
Worked Example
Single-footing example: before waste the footing needs 28.2743 cu ft (1.0472 yd³). With a 10% allowance plan on 31.1017 cu ft (1.1519 yd³) and use the planning bag counts listed above.
Multiple-footing example (4 footings): total before waste 113.0972 cu ft (4.1888 yd³). With 10% waste plan on 124.4068 cu ft (4.6076 yd³). Exact bag totals for four footings: 380 40-lb bags, 252 60-lb bags, or 192 80-lb bags. Planning bag totals with 10%: 416 40-lb bags, 280 60-lb bags, or 208 80-lb bags.
Bag Count Estimate
- 52 bags of 80 lb concrete mix
- 70 bags of 60 lb concrete mix
- 104 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 × 48" 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 | 28.27 | 48 | 63 | 95 |
| +5% typical DIY | 29.69 | 50 | 66 | 99 |
| +10% recommended | 31.1 | 52 | 70 | 104 |
| +15% rough conditions | 32.52 | 55 | 73 | 109 |
When Bagged Concrete vs Ready-Mix Makes Sense
For a single 36" × 48" tube the pour is just over 1 cubic yard, so bags of concrete mix are often simpler: you can carry and mix what you need without calling a truck. The small volume fits into wheelbarrow and mixer workflows and avoids minimum truck charges.
If you have several footings (multiple tubes) and the total climbs into multiple cubic yards, ready-mix becomes more economical and faster on site. Use the planning cubic yards (1.1519 yd³ per footing) to decide when the combined quantity makes a truck delivery sensible.
Common Uses for This Footing Size
This 36" diameter, 48" deep footing is sized for isolated cylindrical supports where the footprint is narrow: pergola posts, deck or porch posts that sit on single tube footings, sign supports, and similar isolated post layouts. The round tube form keeps the footprint compact while giving a deeper bearing element.
Limits come down to load, soil bearing capacity, frost depth at your site, and whether steel reinforcement is required. Those factors determine whether this diameter and depth will work for a particular column or post; your building department or an engineer will tell you if changes are needed.
Common Mistakes to Avoid
Watch for these estimating and planning oversights when ordering for a 36" × 48" round footing.
- Using the exact volume only and forgetting to add a waste allowance.
- Confusing the exact bag counts (95/63/48) with the planning counts (104/70/52).
- Measuring depth to the top of the tube instead of finished footing depth.
- Not multiplying both cubic feet and bag counts when ordering multiple footings.
- Rounding down yardage or bag counts instead of up.
- Failing to confirm reinforcement or building department requirements before final purchase.
Frequently Asked Questions
What is the exact concrete volume for a 36" diameter × 48" deep round footing?
The exact volume is 28.2743 cubic feet, which is 1.0472 cubic yards.
How many bags of concrete do I need for this single footing?
Exact bag counts are 95 40-lb bags, 63 60-lb bags, or 48 80-lb bags. With a 10% allowance plan on 104 40-lb, 70 60-lb, or 52 80-lb bags.
Why include a 10% waste allowance and how is it applied?
The 10% covers spillage, over-excavation, and small measurement errors. Apply it to the exact volume (28.2743 cu ft) to get the planning volume 31.1017 cu ft before converting to bags or yards.
Will a 36" × 48" footing be enough for my deck post or pergola column?
It may work in some cases, but adequacy depends on the actual load, soil bearing capacity, frost depth, and reinforcement. Confirm with your building department or an engineer for the specific support.
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.