Deck Footing Calculator: Concrete and Bags per Pier
A 12 in deck footing 4 ft deep holds 3.14 cubic feet of concrete, which is 6 bags of 80 lb mix with 10% extra.
Advanced options: waste, prices
NRMCA advises ordering 4 to 10 percent over the estimate.
Concrete needed (with 10% extra)
0.13 yd³
0.10 m³ · 3.14 ft³ before extra
Sonotube / column: 12 in × 4 ft. Small pour: premix bags make sense.
Premix bags
- 80 lb6
- 60 lb8
- 50 lb10
- 40 lb12
- Ready-mix cost
- $20
- Weight
- 471 lb
Full breakdown
| Volume before extra | 0.12 yd³ · 0.09 m³ |
|---|---|
| With 10% extra | 0.13 yd³ |
| Weight (150 lb/ft³) | 471 lb · 0.24 tons |
| Pallets of 40 lb (80 bags each) | 1 |
| Pallets of 60 lb (56 bags each) | 1 |
| Pallets of 80 lb (42 bags each) | 1 |
| Truckloads at 12 yd³ | 1 |
| Truckloads at 8 yd³ | 1 |
Bag counts round up, as Quikrete's own calculator does. Cost uses your prices; delivery and short-load fees are extra.
Key takeaways
- Deck footing size: IRC Table R507.3.1 (area per footing + soil).
- A 12 in round footing 4 ft deep = 6 bags of 80 lb.
- Footings go below the frost line (IRC R403.1.4).
- 4,000 psi mix clears the 2,500 psi minimum.
How Much Concrete for Deck Footings?
You need 3.1416 × radius² × depth for each round footing, times the number of footings. A 12 in footing 4 ft deep holds 3.14 ft³; ten of them hold 31.4 ft³, or 1.28 yd³ with 10% extra.
How Many Bags of Concrete per Deck Footing?
| Footing diameter | 3 ft deep (80 lb) | 4 ft deep (80 lb) | 4 ft deep (60 lb) |
|---|---|---|---|
| 8 in | 2 | 3 | 4 |
| 10 in | 3 | 4 | 6 |
| 12 in | 5 | 6 | 8 |
| 16 in | 8 | 11 | 14 |
How Big Should a Deck Footing Be?
Deck footing size depends on the deck area each footing carries and the soil, under 2021 IRC Table R507.3.1. Rows for a 40 psf live load:
| Area per footing | 1,500 psf soil (square / round / thick) | 2,000 psf soil | 3,000 psf soil |
|---|---|---|---|
| 20 sq ft | 10 / 12 / 6 in | 9 / 9 / 6 in | 7 / 8 / 6 in |
| 40 sq ft | 14 / 16 / 6 in | 12 / 14 / 6 in | 10 / 12 / 6 in |
| 60 sq ft | 17 / 19 / 6 in | 15 / 17 / 6 in | 12 / 14 / 6 in |
| 80 sq ft | 20 / 22 / 7 in | 17 / 19 / 6 in | 14 / 16 / 6 in |
| 100 sq ft | 22 / 25 / 8 in | 19 / 21 / 6 in | 15 / 17 / 6 in |
Snow loads above 40 psf need larger footings from the same table; the code permits interpolation but not extrapolation.
How Many Footings Does a Deck Need?
A deck needs one footing under each post in its framing plan; post spacing comes from the beam span tables in IRC Section R507, so the plan sets the count. Add each footing size as a part in the calculator to total the concrete.
Is 4,000 psi Concrete Good for Deck Footings?
Yes, 4,000 psi is above the 2,500 psi minimum the 2021 IRC sets for foundations not exposed to the weather (Table R402.2); Quikrete Concrete Mix is rated at 4,000 psi.
Precast Pier Blocks Instead of Footings
The 2021 IRC lets some free-standing decks skip footings, including decks whose joists bear directly on precast concrete pier blocks at grade and meet the size limits in R507.3; attached decks need footings.
Worked Examples: Footings for Three Decks
12×12 ft deck, 4 posts, 10 in round × 3 ft. 4 × 1.64 ft³; with extra, 12 bags of 80 lb.
16×12 ft deck, 6 posts, 12 in round × 4 ft. 6 × 3.14 ft³; with extra, 35 bags of 80 lb.
20×20 ft deck, 9 posts, 12 in round × 4 ft. 9 × 3.14 ft³; with extra, 1.15 yd³, near the bags-vs-truck point.
How Deep Should Deck Footings Be?
Exterior footings must sit at least 12 in below undisturbed ground and below the local frost line (2021 IRC R403.1.4); deck footings follow Section R507.3.
Should Deck Footings Have Rebar?
The IRC deck footing table sets size, not reinforcement; follow your plans or local code if they call for steel.
Deck Footing Calculator FAQ
How many footings are needed for a 12×12 deck?
One per post in the framing plan, often 4 for a 12×12 ft freestanding deck; beam spans in IRC R507 set the exact count.
Can I use Quikrete for deck footings?
Yes, Quikrete Concrete Mix is rated at 4,000 psi, above the 2,500 psi IRC minimum for footings.
Is 4000 psi concrete good for deck footings?
Yes, it exceeds the 2,500 psi minimum the 2021 IRC sets for footings not exposed to the weather.
What is the best concrete mix for pouring deck footings?
A standard 4,000 psi concrete mix such as Quikrete Concrete Mix or Sakrete High-Strength; it clears the IRC minimum and yields 0.6 ft³ per 80 lb bag.
How strong is 4000 psi concrete after 7 days?
Concrete reaches about 70% of its potential strength at about 7 days, according to Concrete Network, so roughly 2,800 psi for a 4,000 psi mix.
Next step
Size each footing from Table R507.3.1 above, then total all footings as parts and compare bags with ready-mix on when ready-mix beats bags.
Official sources
Last reviewed 2026-11-05. Numbers come from our tested engine; see how we calculate and our sources.