How Much Concrete for a 12x24x48 Footing?
12" x 24" x 48" footing: exact volume, cubic yards, and recommended bag counts including 10% waste
See how a 12×24×48 footing equals 8 cubic feet (0.2963 yd³) of concrete and the planning totals with 10% waste—about 30 40-lb bags or 0.3259 cubic yards.
12" x 24" x 48" describes a rectangular footing that is 1 ft long, 2 ft wide and 4 ft deep. That depth makes this footing suitable for deep frost-protected placements or heavy post loads where a 48-inch embedment is required by local practice.
For residential work this size often appears under deck posts that need deep support, small porch columns, or single-post foundations for light structures. It’s a compact quantity to mix on site with bags of concrete mix or to consider in a small readymix order if local minimums allow.
Quick Answer
This 12" x 24" x 48" footing contains exactly 8.0 cubic feet of concrete, which equals 0.2963 cubic yards. With a standard 10% allowance for waste and spillage, plan on 8.8 cubic feet or about 0.3259 cubic yards.
For ordering by bags, plan on roughly 30 40-lb bags, 20 60-lb bags, or 15 80-lb bags after waste is added. (Exact bag counts without waste are 27 40-lb, 18 60-lb, or 14 80-lb.)
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How to Use This Footing Estimate
Quick way to get this footing poured without surprises:
- Confirm dimensions in inches and convert to feet (1 ft × 2 ft × 4 ft).
- Calculate volume in cubic feet and convert to cubic yards.
- Add a waste allowance (10% used here) to get your planning volume.
- Choose between bagged concrete or readymix based on quantity and local delivery minimums.
- Account for reinforcement, place concrete, consolidate, and follow proper curing times.
- Round bag counts up and buy slightly more if access or spillage is likely.
Formula
The basic formula for a rectangular footing is length × width × depth, all in feet. For this footing: 1.0 ft × 2.0 ft × 4.0 ft = 8.0 cubic feet.
To convert cubic feet to cubic yards divide by 27. So 8.0 cu ft ÷ 27 = 0.296296... which rounds to 0.2963 cubic yards.
Apply a waste factor to cover spillage and slight over-excavation. With 10% waste: 8.0 cu ft × 1.10 = 8.8 cu ft. Convert that to cubic yards: 8.8 ÷ 27 = 0.325925..., which rounds to 0.3259 yd³.
Bag counts are usually derived from the planning volume; the supplied planning figures are 30 40-lb bags, 20 60-lb bags, or 15 80-lb bags for this footing after the 10% allowance.
Worked Example
Single-footing example: this one footing uses 8.0 cubic feet (0.2963 yd³) of concrete. Including 10% waste you will plan for 8.8 cubic feet (0.3259 yd³) and about 30 40-lb bags.
Multiple-footing example: three identical footings = 3 × 8.0 cu ft = 24.0 cu ft total, which is 24.0 ÷ 27 = 0.8889 yd³. With 10% waste plan on 26.4 cu ft total (0.9778 yd³) and about 90 40-lb bags (3 × 30), or 60 60-lb bags (3 × 20), or 45 80-lb bags (3 × 15).
Bag Count Estimate
- 15 bags of 80 lb concrete mix
- 20 bags of 60 lb concrete mix
- 30 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 12" x 24" x 48" footing the volume after waste is only about 0.3259 cubic yards. That small volume often makes bagged concrete the simplest option: you can mix what you need at the site and avoid minimum truck charges.
Readymix gives faster placement and more consistent slump for larger pours, but many plants have minimum order sizes and delivery fees that make a 0.3 yd³ pour inefficient. If you have several footings or other concrete work nearby, readymix can become practical; otherwise bagged concrete mix keeps material costs lower for this quantity.
Also consider labor and finishing: bags require on-site mixing and more physical work, while readymix reduces mixing time and can be easier when placing and consolidating around reinforcement.
Common Uses for This Footing Size
A 12x24x48 footing is commonly used for supporting deck posts, pergola posts, fence posts, and small porch columns. Its rectangular shape and size make it suitable for single-point supports where the load is not very heavy. This footing can help keep posts stable in typical residential settings, especially for structures that don’t carry large amounts of weight or extensive framing.
Whether this footing size will work depends on several factors, including the weight it needs to hold, the type of soil it sits on, how deep the frost line is in your area, and if reinforcement like rebar is needed. Local building codes also play a role in deciding if this footing meets the requirements for your project. It’s important to consider these details before choosing this size for your support needs.
Common Mistakes to Avoid
Common errors to avoid when planning this footing:
- Failing to add a waste allowance — always include at least 10% for small pours.
- Counting exact bag numbers without rounding up — buy whole bags and expect a little extra use.
- Ignoring local frost-depth requirements and permit rules — a 48" depth may still need approval.
- Skipping reinforcement when loads or soil conditions call for rebar or mesh.
- Mistiming placement and finishing — concrete needs consolidation and proper curing time.
- Assuming readymix is always cheaper — check minimums and delivery fees for small volumes.
Frequently Asked Questions
How much concrete is in a 12" x 24" x 48" footing?
The footing contains 8.0 cubic feet of concrete, which is 0.2963 cubic yards. With a 10% waste allowance plan for 8.8 cubic feet or about 0.3259 cubic yards.
How many bags of concrete will I need for this footing?
Exact counts (no waste) are 27 40-lb bags, 18 60-lb bags, or 14 80-lb bags. For planning with 10% waste, use about 30 40-lb bags, 20 60-lb bags, or 15 80-lb bags.
Why should I include waste when ordering concrete?
Including waste accounts for spillage, slight over-excavation, uneven subgrades, and mixing losses. A standard 10% allowance is commonly used for small footings to prevent coming up short.
Is a 12" x 24" x 48" footing big enough for a deck post?
It depends on the deck load, soil bearing capacity, frost depth, and local code requirements. This footing may be suitable where a 48-inch depth aligns with local frost-depth requirements, but check load calculations, reinforcement needs, and your building department before proceeding.
Keep Planning Your Concrete Project
Use the calculator, compare footing pages, and keep your estimate practical before you buy 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.