How to Use This Footing Estimate

Quick steps to get this footing poured correctly:

1. Confirm the footprint and mark the 16" × 16" outline at each footing location.
2. Excavate to 36" deep and check the bottom for firm, undisturbed soil or compacted fill.
3. Calculate concrete needed (use 5.3333 cu ft per footing) and add 10% for waste when ordering or buying bags.
4. Decide mix method: buy bagged concrete or arrange ready‑mix to match the planned 0.2173 yd³ per footing with waste.
5. Place any required reinforcement and formwork, pour or place concrete, then consolidate and finish.
6. Cure the concrete per mix instructions and protect from rapid moisture loss for the first few days.

Formula

The volume of a rectangular (or square) footing is length × width × depth. For this footing the measurements in feet are 1.3333 ft × 1.3333 ft × 3.0 ft.

Multiplying those values gives the exact cubic feet: 1.3333 × 1.3333 × 3 = 5.3333 cubic feet. To convert to cubic yards divide by 27: 5.3333 ÷ 27 = 0.1975 cubic yards.

To allow for spillage, uneven forms, and slight measurement error we add 10% waste: 5.3333 × 1.10 = 5.8666 cubic feet, or 0.2173 cubic yards. Use the waste-adjusted numbers when ordering or buying bagged mixes so you don’t come up short.

Worked Example

Single footing example: one 16" × 16" × 36" footing needs 5.3333 cu ft (0.1975 yd³) of concrete. If you buy bagged mix and include 10% waste, plan for 5.8666 cu ft (0.2173 yd³) — about 20 40‑lb bags, 14 60‑lb bags, or 10 80‑lb bags.

Multiple footings example: three identical footings require 5.3333 × 3 = 15.9999 cu ft (0.5925 yd³). With 10% waste plan for 5.8666 × 3 = 17.5998 cu ft (0.6519 yd³). That equals roughly 60 40‑lb bags, 42 60‑lb bags, or 30 80‑lb bags when you buy bags with waste included.

Bag Count Estimate

• 10 bags of 80 lb concrete mix
• 14 bags of 60 lb concrete mix
• 20 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" × 16" × 36" footing the total concrete volume is under a quarter cubic yard, so buying bags of concrete is often the most practical option. Bagged concrete lets you match small quantities precisely and avoid minimum ready‑mix delivery sizes.

Ready‑mix concrete is convenient when pouring many footings at once or when a continuous pour is needed for reinforcement and consolidation. For one or two footings, bagged concrete reduces waste and logistics; for multiple footings, compare the total planned cubic yards (with waste) to ready‑mix minimum order sizes and choose the most economical, least wasteful option.

Common Uses for This Footing Size

A 16x16x36 footing is commonly used for supporting deck posts, pergola posts, fence posts, and small porch columns. Its size fits well for single-point supports where the load is relatively light. This footing can be placed below ground to help anchor wooden or metal posts that hold up outdoor structures like decks or small covered porches. It’s a practical choice when you need a solid base without going too large or deep.

Whether this footing size is suitable depends on several factors like the weight it needs to carry, the type of soil at your site, how deep the frost line is in your area, and if any reinforcement is needed. Local building codes also play a role in deciding if this footing meets the requirements for your specific project. It’s important to consider these details before proceeding.

Common Mistakes to Avoid

Common mistakes to avoid with this footing size:

• Failing to add a waste allowance and running out mid‑pour.
• Not checking local frost depth and building department requirements before setting depth.
• Skipping or undersizing reinforcement where soil or loads require it.
• Poor subgrade preparation — leaving loose soil at the bottom of the excavation.
• Using the wrong bag type or mix strength for the intended load.
• Not consolidating the concrete properly, which can leave voids under the footing.