How to Use This Footing Estimate

Quick steps to estimate and order concrete for this 8" × 36" round footing.

1. Measure the inside diameter of the tube and confirm the tube is 8" across and 36" tall.
2. Use the cylinder volume check (see formula block) to confirm the 1.0472 cu ft figure.
3. Add a waste allowance — this page uses 10% (1.1519 cu ft planning volume).
4. Decide bagged mix or ready-mix based on how many footings you have.
5. Multiply bag counts for multiple footings and round up to whole bags when ordering.
6. Account for any reinforcement or concrete placed below the tube that changes the volume.

Formula

Use this round footing formula:

If you add a 10% waste allowance, you should plan closer to 0.04 cubic yards.

Worked Example

Single-footing example — before waste: 1.0472 cu ft (0.0388 cu yd). With 10% waste: 1.1519 cu ft (0.0427 cu yd). Bag counts for one footing: exact 4 40-lb / 3 60-lb / 2 80-lb; with 10% waste plan on the same listed bag totals.

Multiple-footing example — four identical footings: total before waste = 4.1888 cu ft (0.1552 cu yd). With 10% waste the total is 4.6076 cu ft (0.1708 cu yd). Planning bag totals for four footings: 16 40-lb bags, 12 60-lb bags, or 8 80-lb bags.

Bag Count Estimate

• 2 bags of 80 lb concrete mix
• 3 bags of 60 lb concrete mix
• 4 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 8" × 36" footing, bagged concrete is often simpler: a couple of bags mixed on-site and a small wheelbarrow pour. You avoid waiting for a truck and you buy only the number of bags you need.

If you have several of these footings (for example four or more) the volumes add up. At that point get a ready-mix quote and compare cost and timing against buying dozens of bags and mixing multiple batches.

Common Uses for This Footing Size

This 8" diameter × 36" deep footing is typically used for isolated post supports in narrow layouts — pergola posts, small deck or stair posts, sign posts, and other cylindrical footing layouts where the footprint needs to be small. It fits a narrow tube form and keeps the pour volume low.

Limits matter: actual suitability depends on the applied load, soil bearing capacity, frost depth at the site, whether you add reinforcement, and permit requirements. Confirm frost depth and permit rules with your municipal building department and size reinforcement accordingly.

Common Mistakes to Avoid

Common estimating and ordering mistakes to watch for.

• Mixing outside vs inside diameter: use the inside diameter of the form when computing volume.
• Forgetting to add a waste allowance — small pours still need extra for spillage and uneven tubes.
• Rounding down bag counts instead of rounding up to whole bags.
• Assuming every tube is perfectly vertical or full — check actual tube height after setting.
• Not totaling quantities correctly when ordering multiple footings.
• Ordering the wrong bag size and miscounting how many smaller bags you need.