How Much Concrete for a 12x12x48 Footing?
How much concrete and how many bags for a 12" x 12" x 48" footing — cubic feet, cubic yards, and bag planning counts.
Calculate material for a single 12" × 12" × 48" concrete footing: exact volume in cu ft and yd³, plus planning numbers including 10% waste and bag counts for 40-, 60-, and 80-lb mixes.
Start with the materials: this 12" × 12" × 48" (1 ft × 1 ft × 4 ft) concrete footing contains 4.00 cubic feet of concrete, or about 0.1481 cubic yards. If you’re buying bagged concrete, the exact counts are 14 40-lb bags, 9 60-lb bags, or 7 80-lb bags; plan for slightly more to allow for waste.
This size suits isolated column footings, single-post foundations, or small structural supports where a deep footing is needed for bearing. Before you build, have the design and reinforcement reviewed for your load case and check with a structural engineer or building department if you’re unsure about sizing, reinforcement, or permit requirements.
Quick Answer
Exact volume: 4.00 cubic feet (0.1481 cubic yards). With a 10% waste allowance, plan on 4.40 cubic feet (0.1629 cubic yards).
Bag planning counts with 10% waste: about 15 40-lb bags, 10 60-lb bags, or 8 80-lb bags. The exact (no-waste) counts are 14 40-lb, 9 60-lb, or 7 80-lb bags.
Need a custom estimate? Use the Footing Calculator. Browse footing size pages. All project pages.
How to Use This Footing Estimate
Basic steps to pour a 12" × 12" × 48" footing using bagged concrete:
- Measure and mark the footing location; dig to the full 48" depth and check dimensions are 12" × 12" at the footing plane.
- Compact the bottom and add a few inches of gravel if required for drainage and bearing.
- Set formwork square and braced to hold a 12" × 12" cross section for the full depth.
- Mix bagged concrete to the manufacturer’s directions and pour in lifts, avoiding large voids.
- Place any required reinforcement (rebar or dowels) per the engineer’s detail before full pour.
- Strike off and finish the top so the footing seats the column base; keep concrete moist for the recommended curing period.
- Schedule inspection or have an engineer verify reinforcement and dimensions before covering the footing.
Formula
Volume of a rectangular footing is length × width × depth. Convert all dimensions to feet: 12" = 1.0 ft, 12" = 1.0 ft, 48" = 4.0 ft. So the volume is 1.0 ft × 1.0 ft × 4.0 ft = 4.00 cubic feet.
Convert cubic feet to cubic yards by dividing by 27 (there are 27 cubic feet in a cubic yard): 4.00 ÷ 27 = 0.148148… which we report as 0.1481 cubic yards.
Include a waste allowance (10% here): 4.00 cu ft × 1.10 = 4.40 cu ft, and 0.1481 yd³ × 1.10 = 0.1629 yd³. Bag counts are then determined from typical bag yields—here the provided exact counts for the 4.00 cu ft volume are 14 40-lb bags, 9 60-lb bags, or 7 80-lb bags; with 10% waste plan on 15, 10, or 8 bags respectively.
Worked Example
Single footing example: one 12" × 12" × 48" footing requires 4.00 cubic feet (0.1481 yd³). That equals 14 40-lb bags exact, or plan on 15 40-lb bags with the 10% waste allowance.
Multiple footings example: three identical footings need 3 × 4.00 = 12.00 cubic feet total, which is 12.00 ÷ 27 = 0.4444 cubic yards. For three footings you’d use 42 40-lb bags exact, or plan on 45 40-lb bags with the 10% waste allowance (similarly multiply the 60-lb and 80-lb counts by 3: exact 27 60-lb or 21 80-lb; planning 30 60-lb or 24 80-lb bags).
Bag Count Estimate
- 8 bags of 80 lb concrete mix
- 10 bags of 60 lb concrete mix
- 15 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" × 12" × 48" footing (0.1481 yd³) bagged concrete is often the most practical choice—you can buy the 15 40-lb bags you need, mix on site, and avoid a truck minimum. Bagged concrete keeps costs predictable for one or two footings and lets you control mix water and placement when access is tight.
Ready-mix becomes more attractive when pouring multiple footings, tight schedules, or when you prefer a uniform mix and less on-site labor. Keep in mind most ready-mix suppliers have a minimum order (often well over 0.15 yd³), so for three or more footings the convenience and consistency of a small ready-mix delivery can outweigh the setup and mixing time of many bags.
Common Uses for This Footing Size
A 12x12x48 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 isn’t very heavy. This footing can be set below ground to help keep posts stable and prevent shifting over time. It’s often chosen for residential projects where the structure is light and the footing doesn’t need to spread out a large load.
Whether this footing size is right depends on several factors like how much weight the post will carry, the type of soil, how deep the frost line is in your area, and if any reinforcement is needed. Local building codes also play a role in what size and depth are allowed or recommended for your project.
Common Mistakes to Avoid
Common mistakes to avoid when pouring this footing size:
- Ordering exactly 4.00 cu ft with no allowance—always include waste.
- Failing to compact or provide a gravel pad at the footing bottom.
- Skipping required reinforcement or not following the engineer’s dowel pattern.
- Overwatering mixes during on-site bag mixing and weakening the concrete.
- Poor formwork that moves or bulges under the pour.
- Not curing the concrete properly—keep it moist for the recommended time.
Frequently Asked Questions
How much concrete volume is in a 12x12x48 footing?
The footing contains 4.00 cubic feet of concrete, which is 0.1481 cubic yards.
How many bags of concrete do I need for this footing?
Exact counts for the 4.00 cu ft volume are 14 40-lb bags, 9 60-lb bags, or 7 80-lb bags. Plan for waste: about 15 40-lb, 10 60-lb, or 8 80-lb bags.
Why should I add waste to my concrete order?
Add about 10% for waste to cover spillage, over-excavation, slight measurement errors, and finishing—this footing uses 4.40 cu ft (0.1629 yd³) with that allowance.
Is a 12x12x48 footing adequate for a deck post?
It depends on the post load, local soil bearing capacity, frost depth, and code requirements. This footing’s volume and depth may work for many posts, but confirm loads and reinforcement with a structural reviewer or building department before relying on it.
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.