How to Use This Footing Estimate

Follow these steps to prepare and pour a single 16" x 16" x 24" footing.

1. Excavate to the planned 24" depth and check that the bottom is level and compacted.
2. Measure the footprint to confirm 16" by 16" and verify depths with a level or tape.
3. Calculate concrete needed (3.5556 cu ft per footing) and add 10% for cutting and waste.
4. Decide on bagged mix or ready-mix and gather bags, water, reinforcement, and form material.
5. Mix or receive concrete, place it in the form, consolidate to remove voids, and finish the top surface.
6. Cure the concrete per product directions and protect from rapid drying or freezing during the first days.

Formula

The basic formula for a rectangular footing is length × width × depth. Convert each dimension to feet first: 16" = 1.3333 ft, 16" = 1.3333 ft, 24" = 2 ft.

Multiply the converted dimensions: 1.3333 ft × 1.3333 ft × 2 ft = 3.5556 cubic feet. Convert cubic feet to cubic yards by dividing by 27: 3.5556 cu ft ÷ 27 = 0.1317 cubic yards.

To allow for waste and small measurement errors add 10%: 3.5556 cu ft × 1.10 = 3.9112 cu ft, and 0.1317 yd³ × 1.10 = 0.1449 yd³. The planning bag counts reflect that increased volume.

Worked Example

Single footing example: one 16" x 16" x 24" pad needs 3.5556 cubic feet (0.1317 cubic yards). With 10% waste plan for 3.9112 cu ft (0.1449 yd³) — about 14 40-lb bags, 9 60-lb bags, or 7 80-lb bags.

Multiple footings example: three identical footings use 3 × 3.5556 = 10.6668 cubic feet total, which equals 10.6668 ÷ 27 = 0.3951 cubic yards. With 10% waste multiply the total cubic feet: 10.6668 × 1.10 = 11.7335 cu ft (0.4346 yd³), and plan on roughly 3 × 14 = 42 40-lb bags if using bagged concrete.

Bag Count Estimate

• 7 bags of 80 lb concrete mix
• 9 bags of 60 lb concrete mix
• 14 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" x 16" x 24" footing the concrete volume is small: 0.1317 cubic yards (0.1449 yd³ with waste). That makes bagged concrete a practical option since you can mix only what you need by the bag.

Ready-mix is convenient when you have several footings or larger combined volume because suppliers typically set a minimum delivery (often 1/2 yard or more). If you have multiple footings and the total clips into a half-yard or full-yard increment, ready-mix can save time and deliver consistent mix quality.

Common Uses for This Footing Size

A 16x16x24 footing is commonly used for supporting posts in residential projects where the loads are relatively light. You might see this size footing under deck posts, pergola posts, fence posts, or small porch columns. Its square shape and dimensions make it suitable for single-point supports that don’t carry heavy weight but need a solid base to prevent settling or shifting.

Whether this footing size is appropriate depends on several factors like the weight it needs to hold, the type of soil, how deep the frost line is in your area, and whether reinforcement like rebar is necessary. Local building codes also play a big role in determining if this footing meets the requirements for your specific project.

Common Mistakes to Avoid

Avoid these common mistakes when planning a 16" x 16" x 24" footing.

• Underestimating the needed volume and running out of material mid-pour.
• Skipping the 10% waste allowance and failing to account for spillage or over-excavation.
• Not checking or improving the soil bearing capacity before pouring the footing.
• Failing to place proper reinforcement or using undersized rebar for the expected load.
• Pouring on an uncompacted or uneven base, which can cause settlement.
• Ignoring local building department requirements or permit conditions for footings and loads.