Enter the footing size to see how much concrete it takes, in cubic yards and bags.
How footing concrete is calculated
Round footing: π × (diameter ÷ 2)² × depth
Continuous footing: length × width × depth
Cubic yards = cubic feet ÷ 27
Worked examples
- Four deck footings in 12 in tubes, 48 in deep: π × 0.5² × 4 = 3.14 cu ft each, 12.57 cu ft in total (0.47 cu yd), or 21 bags of 80 lb before extra.
- A 40 ft wall footing 16 in wide and 8 in deep: 40 × 1.333 × 0.667 = 35.6 cu ft, or 1.32 cu yd.
Common form tube sizes
| Tube diameter | Concrete per foot of depth | 80 lb bags per foot |
|---|
| 8 in | 0.35 cu ft | 0.58 |
| 10 in | 0.55 cu ft | 0.91 |
| 12 in | 0.79 cu ft | 1.31 |
| 16 in | 1.40 cu ft | 2.33 |
Limitations
- Size and depth come from code: footings must go below your area's frost line and be sized for the load. Check your plans and local building department.
- Bell-shaped or flared footings hold more concrete than a straight tube.
Sources
How we checked this
Before every update, this calculator is run in a real browser with these known answers, and it must match all of them:
- Four 12 in tubes, 48 in deep, no extra: 0.4654 cubic yards ✓
- Same: 21 bags of 80 lb ✓
- 40 ft × 16 in × 8 in wall footing: 1.317 cubic yards ✓
- Edge: 0 footings asks for at least 1 ✓
Last checked October 26, 2026. Spotted something wrong? The math is done in your browser with the formula shown on this page, so you can check any result by hand.
Questions people ask
How much concrete do I need for a 12 inch Sonotube?
About 0.79 cubic feet per foot of depth, so a 4 ft tube takes 3.14 cubic feet: about 5.2, so 6, bags of 80 lb.
How many bags of concrete per footing?
A 12 in round footing 4 ft deep takes about 6 bags of 80 lb mix with a little extra.
How deep should deck footings be?
Below your local frost line, which varies from a few inches in the South to 4 feet or more in the North. Ask your building department.
How do you calculate concrete for a footing?
Multiply length × width × depth in feet for a rectangle, or π × radius² × depth for a round footing, then divide by 27 for cubic yards.