How much concrete for deck footings?
Quick Answer
A standard 12-inch diameter deck footing 42 inches deep (typical frost depth) requires about 2.5 bags of 80-lb concrete mix per footing. A typical 12ร16-foot deck with 6 footings needs 15 bags total. Larger 16-inch diameter footings use 4โ5 bags each.
Quick Reference Table
| Footing diameter ร depth | Concrete bags per footing |
|---|---|
| 10" dia ร 36" deep | 1.5 bags (80-lb) |
| 12" dia ร 42" deep | 2.5 bags (80-lb) |
| 12" dia ร 48" deep | 3 bags (80-lb) |
| 16" dia ร 42" deep | 4.5 bags (80-lb) |
| 16" dia ร 48" deep | 5 bags (80-lb) |
How to Calculate It Yourself
- 1
Find your local frost depth (required footing depth) โ usually 36โ48" in northern states.
- 2
Choose footing diameter: minimum 10" for typical decks, 12โ16" for heavy spans.
- 3
Calculate volume: ฯ ร (radius)ยฒ ร depth (all in feet).
- 4
12" dia ร 42" deep: ฯ ร 0.25 ร 3.5 = 2.75 cu ft รท 0.60 cu ft/bag = 4.6 bags.
- 5
Multiply by number of footings and add 10% for spillage.
Pro Tip
Use Quikrete Fast-Setting Concrete for deck footings โ pour it dry, add water on top, no mixing needed. Set time is 20โ40 minutes and you can install posts the same day.
Assumptions to Check
Before ordering materials, confirm the dimensions, product coverage, waste factor, and local installation requirements for your project. Manufacturer coverage tables and local code rules can change the final quantity, especially for structural work, exterior projects, and irregular layouts.
Need an exact number for your specific dimensions?
Use the Concrete Calculator โ