Calculate Concrete for Footings
Select your footing type and enter dimensions to calculate concrete volume, bags needed, and estimated cost.
Continuous (Strip) Footing
Pier (Column) Footing
Spread (Pad) Footing
Bags of Concrete Needed
Cost Estimator
Common Footing Sizes by Use Case
Standard footing dimensions for residential and light commercial construction. Always verify with local building codes and a structural engineer for your specific project.
| Use Case | Footing Type | Width | Depth | Notes |
|---|---|---|---|---|
| 1-Story House Wall | Continuous | 12 in (30 cm) | 6 in (15 cm) | Minimum for light-frame construction |
| 2-Story House Wall | Continuous | 15-16 in (38-41 cm) | 8 in (20 cm) | Wider to support additional load |
| 3-Story House Wall | Continuous | 18-24 in (46-61 cm) | 8-10 in (20-25 cm) | Engineer-designed recommended |
| Garage Wall | Continuous | 12-16 in (30-41 cm) | 8 in (20 cm) | Match house footing width |
| Deck Post (low) | Pier | 12 in dia (30 cm) | 24-36 in (61-91 cm) | Below frost line, check local codes |
| Deck Post (elevated) | Pier | 16-18 in dia (41-46 cm) | 36-48 in (91-122 cm) | Larger for heavy loads or tall decks |
| Fence Post | Pier | 8-10 in dia (20-25 cm) | 24-36 in (61-91 cm) | 1/3 of total post length below grade |
| Column Support | Spread | 24 x 24 in (61 x 61 cm) | 10-12 in (25-30 cm) | For point loads on interior columns |
| Porch Post | Spread | 18 x 18 in (46 x 46 cm) | 8-10 in (20-25 cm) | Under porch columns or posts |
| Heavy Equipment Pad | Spread | 36 x 36 in (91 x 91 cm) | 12-16 in (30-41 cm) | For HVAC units, generators, etc. |
How Footing Calculations Work
Continuous (Strip) Footings
Volume = Length x Width x Depth. These run along the perimeter of walls and distribute the load of the structure linearly to the ground. Width is typically twice the wall thickness. The footing must extend below the frost line to prevent heaving.
Pier (Column) Footings
Volume = pi x (Diameter/2)^2 x Depth. Cylindrical footings support individual posts or columns, commonly used for decks, porches, and fence posts. Sonotube forms make pouring easy. Multiply by the number of piers for total volume.
Spread (Pad) Footings
Volume = Length x Width x Depth. Square or rectangular pads that spread a concentrated load over a wider area. Used under columns, posts, and point loads. Size depends on soil bearing capacity and the load being supported.
Waste Factor
Always add 10-15% extra concrete to account for spillage, uneven excavation, and over-digging. Use 10% for simple rectangular shapes and 15% for irregular excavations. Running short mid-pour creates a cold joint that weakens the footing.
Bags vs. Ready-Mix: When to Use Each
Use Bagged Concrete When...
Your project needs less than 1-2 cubic yards. Common for pier footings, small pad footings, and fence posts. You can mix at your own pace and pour one section at a time. An 80-lb bag yields about 0.6 cubic feet of concrete.
Use Ready-Mix (Truck) When...
Your project needs more than 2 cubic yards. Continuous wall footings for a house typically require 3-10+ cubic yards. Ready-mix costs $100-$150 per yard and arrives pre-mixed, saving hours of labor. Minimum order is usually 1 yard with possible short-load fees.
Concrete Bag Coverage Reference
| Bag Size | Coverage (cu yd) | Coverage (cu ft) | Bags per cu yd | Approx. Cost per Bag |
|---|---|---|---|---|
| 40 lb (18 kg) | 0.011 | 0.30 | 90 | $3.50 - $5.00 |
| 60 lb (27 kg) | 0.017 | 0.45 | 59 | $4.50 - $6.00 |
| 80 lb (36 kg) | 0.022 | 0.60 | 45 | $5.50 - $7.50 |
Frequently Asked Questions
How much concrete do I need for a footing?
How deep should a concrete footing be?
What is the difference between continuous, pier, and spread footings?
How many bags of concrete do I need for a footing?
What is the standard size for a residential footing?
Can I pour footings in sections?
Privacy & Limitations
All calculations are performed locally in your browser. No data is sent to our servers. This calculator provides estimates based on standard concrete densities and bag coverage rates. Actual amounts may vary based on concrete mix, moisture content, soil conditions, and excavation accuracy. Always consult with a structural engineer and check local building codes for critical foundation work.
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Concrete Footing Calculator FAQ
How much concrete do I need for a footing?
Calculate volume by multiplying length x width x depth. For a continuous footing 30 ft long, 18 in wide, and 8 in deep, the volume is 30 x 1.5 x (8/12) = 30 cubic feet, or about 1.11 cubic yards. Add 10-15% for waste.
How deep should a concrete footing be?
Footing depth depends on the structure and local building codes. Residential footings are typically 8-12 inches deep. The footing must extend below the frost line, which varies by region from 12 inches in warm climates to 48+ inches in cold climates.
What is the difference between continuous, pier, and spread footings?
Continuous (strip) footings run along the length of a wall and distribute load linearly. Pier (column) footings are cylindrical and support individual posts or columns. Spread footings are square or rectangular pads that distribute point loads over a wider area.
How many bags of concrete do I need for a footing?
Divide total cubic yards by bag coverage. A 40-lb bag covers 0.011 cu yd (about 90 bags per yard). A 60-lb bag covers 0.017 cu yd (about 59 bags per yard). An 80-lb bag covers 0.022 cu yd (about 45 bags per yard). For large footings, ready-mix delivery is more practical.
What is the standard size for a residential footing?
Standard residential wall footings are typically twice the width of the wall they support (e.g., 16 inches wide for an 8-inch wall) and 8 inches deep. Pier footings for decks are usually 12-18 inches in diameter and 12-42 inches deep depending on frost depth.