Concrete Footing Calculator
Calculate concrete for footings, piers, and post holes - in cubic yards and bags.
Your Footing Estimate
- Choose units - Imperial (feet, inches) or Metric (meters, mm).
- Enter dimensions - length and width of the footing or diameter for round piers. Use presets for common depths.
- Select depth - 12 inches is standard for most residential footings. Check your local frost line depth.
- Set waste factor - 10% is typical. Use 15% for irregular excavations or rocky soil.
- Review estimate - for multiple footings, multiply the result by the number of piers or footing sections.
A typical 16 in wide, 8 in thick continuous wall footing takes about 0.033 cubic yards of concrete per linear foot - roughly one 80 lb bag every 8 inches of run. A 20 ft run is about 0.66 cubic yards or 30 bags of 80 lb mix before waste. Round pier footings run far less: a 12 in diameter pier at 36 in deep is about 4 bags of 80 lb mix. Enter your footing dimensions above for the exact volume and bag count.
The Three Measurements a Footing Needs
Footing Concrete Formulas
Rectangular and continuous footings use simple volume math. Round piers use the cylinder formula:
Round pier = π × (Diameter/2)² × Depth
Cubic Yards = Volume (ft³) ÷ 27
Bags (80 lb) = Volume (ft³) ÷ 0.6
With Waste = Volume × (1 + Waste %)
For Sonotube or cardboard form tubes, measure the inside diameter. The calculator uses the same cylinder formula.
How Deep Should Footings Be?
Footing depth is primarily determined by your local frost line - the depth at which soil freezes in winter. Footings poured above the frost line can heave and crack as the ground freezes and thaws. Most building codes require the bottom of the footing to sit at least 12 inches below the frost line.
In the southern US, frost lines are typically 6 to 12 inches deep. In the northern US and Canada, frost lines can reach 48 to 72 inches. Always check with your local building department before digging - the inspector will verify depth before allowing a pour.
Footing Sizes by Structure
Standard residential footing dimensions depend on what they support. Wider footings spread the load over more soil:
| Structure | Footing Width | Footing Depth | Notes |
|---|---|---|---|
| Deck post (4×4) | 12" diameter | 36–48" | Sonotube or pre-cast pier |
| Fence post | 8–10" diameter | 24–36" | Below frost line |
| Shed / small outbuilding | 12" × 12" | 12" | On compacted gravel |
| Residential wall | 16–20" wide | 8–12" | Width = 2× wall thickness |
| Garage / addition | 20–24" wide | 12" | Below frost line; rebar required |
| Retaining wall | 24–36" wide | 12–18" | Engineer-specified for height > 4 ft |
These are general guidelines. Your engineer or building code may require different dimensions based on soil bearing capacity and structural loads.
Concrete per Round Pier (Common Sonotube Sizes)
| Tube Diameter | Depth 36" | Depth 48" | Depth 60" |
|---|---|---|---|
| 8" | 0.058 yd³ (3 bags) | 0.078 yd³ (4 bags) | 0.097 yd³ (5 bags) |
| 10" | 0.091 yd³ (5 bags) | 0.121 yd³ (7 bags) | 0.152 yd³ (8 bags) |
| 12" | 0.131 yd³ (7 bags) | 0.175 yd³ (9 bags) | 0.218 yd³ (12 bags) |
| 14" | 0.178 yd³ (10 bags) | 0.238 yd³ (13 bags) | 0.297 yd³ (16 bags) |
| 16" | 0.233 yd³ (13 bags) | 0.310 yd³ (17 bags) | 0.388 yd³ (21 bags) |
Bag count based on 80 lb bags (0.6 ft³ each). Includes no waste - add 10% to your order.
Footing concrete cost by project (2026)
| Footing type | Concrete needed | Material cost | Contractor installed |
|---|---|---|---|
| Fence post (8-in tube, 2 ft deep) | 0.06 yd3 | $8-$12 per post | $25-$50 per post |
| Deck pier (12-in tube, 3 ft) | 0.11 yd3 | $14-$20 per pier | $60-$120 per pier |
| Deck pier (16-in tube, 4 ft) | 0.26 yd3 | $33-$47 per pier | $100-$200 per pier |
| Strip footing (per linear ft, 12x8 in) | 0.025 yd3 | $4-$6 per lin ft | $15-$35 per lin ft |
| Continuous footing (100 lin ft) | 2.5 yd3 | $400-$600 total | $1,500-$3,500 total |
| Pad footing (3x3 ft, 1 ft deep) | 0.33 yd3 | $55-$80 each | $200-$450 each |
Material based on ready-mix at $150-$200/yd or bags at $6-$8 per 80 lb. Contractor pricing includes excavation, forming, and pouring. Northern states require deeper footings below frost line (30-48 in) which increases cost significantly.
Related Calculators
Code & Source Notes
- Residential spread footings must be at least 6 inches thick, and the footing projection past each face of the wall must be at least 2 inches but not more than the footing thickness. Minimum footing width depends on the construction type, stories supported, and soil bearing value per the code tables.IRC R403.1.1 - Minimum Footing Size
- Footing bottoms must extend below the local frost line on undisturbed natural soil or engineered fill. Frost depth is set by the local jurisdiction - verify it with your building department before digging.IRC R403.1 - General (Footings)
After You Size the Footing
Footing volume is the first number of the foundation stage. The usual order from here:
Footings support slabs, posts, and walls. Browse the construction calculator collection for all concrete tools.