Deck Footing Concrete Calculator
Footings are cylinders of concrete, so the math is πr²h per pier. Enter your pier count, diameter and depth to get total volume and bag count.
Result
- Concrete per footing3.14cu ft
- Total concrete (with waste)31.1cu ft
- Total concrete1.15cu yd
- 50 lb bags needed83bags
- Metric0.88m³
How it works
volume = π × (diameter/2)² × depth, per footing × count × (1 + waste)
- Radius = 12 in ÷ 2 ÷ 12 = 0.5 ft
- Depth = 48 in ÷ 12 = 4 ft
- One pier = π × 0.5² × 4 = 3.142 cu ft
- 9 footings + 10% waste = 31.102 cu ft
- 50 lb bags at 0.375 cu ft each = ceil(31.102 ÷ 0.375) = 83 bags
How the deck footing concrete calculator works
A pier footing is a cylinder: volume equals π times the radius squared times the height. Convert inches to feet first, then multiply.
Add waste — 10% is sensible for pour-off and uneven holes. Then divide by the yield printed on the concrete bag: about 0.375 cu ft for 50 lb, 0.45 for 60 lb and 0.60 for 80 lb bags.
Footing depth is not a free choice. Most jurisdictions require the bottom of the footing to sit below the frost line, which ranges from a few inches in mild climates to 48 inches or more in cold ones.
Formula
volume = π × (diameter ÷ 2)² × depth, per footing × count × (1 + waste)
Worked example: 6 piers, 12" diameter, 48" deep
- Radius = 12 ÷ 2 ÷ 12 = 0.5 ft
- Depth = 48 ÷ 12 = 4 ft
- One pier = π × 0.5² × 4 = 3.14 cu ft
- 6 piers + 10% waste = 20.73 cu ft
- 50 lb bags at 0.375 cu ft each = ceil(20.73 ÷ 0.375) = 56 bags
Concrete per pier (before waste)
| Diameter | 36" deep | 48" deep | 60" deep |
|---|---|---|---|
| 8" | 1.05 cu ft | 1.40 cu ft | 1.75 cu ft |
| 10" | 1.64 cu ft | 2.18 cu ft | 2.73 cu ft |
| 12" | 2.36 cu ft | 3.14 cu ft | 3.93 cu ft |
| 16" | 4.19 cu ft | 5.59 cu ft | 6.98 cu ft |
πr²h. A 50 lb bag yields about 0.375 cu ft — always follow the yield printed on your bag.
Frequently asked questions
How much concrete do I need for a 12 inch diameter footing?
At 48 inches deep, one 12" pier takes 3.14 cu ft — about 9 bags of 50 lb concrete (0.375 cu ft yield each), or 7 bags of 80 lb. Multiply by your pier count and add 10% waste.
How many bags of concrete per deck footing?
For a common 12" × 48" pier: 9 bags of 50 lb, 7 of 60 lb or 6 of 80 lb, before waste. Smaller 8" × 36" footings need about 3 bags of 50 lb.
How deep should deck footings be?
Below the frost line in your area — anywhere from 12" in mild climates to 48"+ in cold ones. Beyond frost depth, footings must also reach competent soil per your local code.
Should I use ready-mix or bagged concrete for footings?
Bagged concrete is practical for up to roughly 10–15 piers. Beyond that, a ready-mix truck with a pump or chute is usually cheaper per yard and far less labor. Short-load minimums may apply.