Concrete footings are the critical foundation elements that transfer structural loads to the ground. Whether you're building deck footings, column foundations, or pier pads, accurately calculating concrete volume prevents project delays and ensures structural integrity. Our free footing calculator provides precise estimates for any size footing.

Simply enter the footing length, width, depth, and quantity, and our calculator instantly provides the total volume in cubic yards—the standard unit for ordering concrete.

What Footings Do

Footings serve several critical functions:

1. Distribute loads: Spread concentrated loads over larger soil area

2. Prevent settling: Provide stable base to minimize differential settlement

3. Resist uplift: Anchor structures against wind and seismic forces

4. Transfer weight: Move building weight to competent soil or bedrock

Types of Footings

Spread Footings

• Most common type
• Square or rectangular
• Distributes load over soil bearing area
• Used for columns, piers, posts

Continuous Footings

• Long linear footings
• Support foundation walls
• Running perimeter footings
• Entire building length

Isolated Footings

• Individual column footings
• Independent pads
• Not connected to other footings

Deck Footings

Typical sizing guidelines:

| Deck Size/Load | Footing Size | Footing Thickness |

|----------------|--------------|-------------------|

| Small deck, light roof | 12×12 inches | 6-8 inches |

| Standard residential deck | 16×16 inches | 8 inches |

| Large deck or hot tub | 20×20 inches | 8-10 inches |

| Multi-level deck | 24×24 inches | 10-12 inches |

Spacing considerations:

• Standard spacing: 6-8 feet on center
• Heavy loads: 4-6 feet on center
• Always follow design requirements

Column Footings

Size based on column size:

| Column Size | Minimum Footing | Typical Footing |

|-------------|-----------------|-----------------|

| 8×8 | 20×20 | 24×24 |

| 10×10 | 24×24 | 28×28 |

| 12×12 | 28×28 | 32×32 |

| 16×16 | 36×36 | 40×40 |

Rule of thumb: Footing should be 2-2.5 times column width in each direction.

Pier and Pad Footings

Common applications:

• Porch supports
• Pergola posts
• Garden structures
• Equipment pads

Typical sizes:

• Light structures: 18×18 × 6 inches
• Medium loads: 24×24 × 8 inches
• Heavy loads: 30×30 × 10 inches

The Formula

Footing Volume = Length × Width × Depth

For square footings: Volume = Side² × Depth

Example Calculations

Single 24×24×8 inch footing:

• Volume: 2 × 2 × 0.67 = 2.67 cubic feet
• Cubic yards: 0.10 cubic yards
• 80lb bags: 5 bags

Six 16×16×10 inch deck footings:

• Each: 1.33 × 1.33 × 0.83 = 1.47 cubic feet
• Total: 8.82 cubic feet
• Cubic yards: 0.33 cubic yards
• 80lb bags: 15 bags

Four 30×30×12 inch column footings:

• Each: 2.5 × 2.5 × 1 = 6.25 cubic feet
• Total: 25 cubic feet
• Cubic yards: 0.93 cubic yards
• 80lb bags: 42 bags

Always add extra concrete to account for:

• Over-excavation and uneven hole bottoms
• Soil displacement during pouring
• Spillage during transport from mixer to forms
• Variations in actual vs. planned footing dimensions

Recommended waste factors:

• Individual footings (1-3): 15-20% (small volumes magnify errors)
• Multiple footings (4+): 10-15%
• Sonotube/pier footings: 10%

Ready-Mix vs. Bags for Footings

The right choice depends on the total volume and number of footings:

• Use bags for: a few deck footings or fence posts (under 1 cubic yard total). A single 16×16×10 inch footing needs only about 2-3 bags.
• Order ready-mix for: foundation footings, large decks with 8+ footings, or any project totaling 2+ cubic yards. Six footings at 0.33 cubic yards each already approach the practical limit for hand-mixing.

Frost Depth

Critical consideration:

• Footings must extend below frost line
• Prevents heaving from freeze-thaw cycles
• Varies by climate zone

Typical frost depths:

• Southern states: 12-18 inches
• Mid-Atlantic: 24-30 inches
• Northern states: 36-48 inches
• Extreme northern: 48-60+ inches

Soil Bearing Capacity

General guidelines:

| Soil Type | Bearing Capacity (psf) | Notes |

|-----------|------------------------|-------|

| Solid rock | 12,000+ | Excellent, may reduce footing size |

| Gravel/compact sand | 5,000-8,000 | Good bearing |

| Dense sand | 4,000-6,000 | Good bearing |

| Silty sand | 2,000-4,000 | Fair bearing |

| Clay | 1,500-3,000 | Poor to fair, may need larger footings |

| Soft clay/silt | <1,000 | Poor, requires engineering |

Poor soil solutions:

• Increase footing size
• Use deeper footings
• Engage engineered solutions
• Consider pile foundations

Rebar Requirements

Standard practice:

• #4 rebar at 12-18 inches each way
• Chairs or dobies to position rebar
• 3 inches clearance from soil
• Reinforcement both directions

For heavy loads:

• #5 rebar at 12 inches each way
• Additional top mat for very large footings
• Engineering required for significant loads

Dowels for Columns

Column connections:

• Extend vertical bars into footing
• Minimum: 4 #4 bars
• 12-inch minimum embedment
• Hooked ends or hooked into footing

Concrete Strength

Recommended strengths:

• Standard footings: 3000 psi
• Heavy loads: 3500-4000 psi
• Seismic areas: 4000 psi minimum

Excavation

Best practices:

• Excavate to proper depth
• Level and compact soil bottom
• Remove organic material
• Extend excavation for formwork if needed
• Check for proper bearing soil

Formed vs. Unformed Footings

Formed footings:

• Above-grade portions
• Clean edges
• Precise dimensions
• Requires lumber and labor

Unformed (earth-formed):

• Below-grade only
• Soil acts as form
• Less expensive
• Ensure soil doesn't collapse

Hybrid approach:

• Form only top portion
• Bottom is soil-formed
• Good compromise

Preparation

Before pouring:

• Verify dimensions and depth
• Place rebar on chairs
• Check form alignment
• Clean debris from excavation
• Verify no water in hole

Pouring Technique

Best practices:

• Pour continuously if possible
• Consolidate with vibrator
• Don't pour through rebar from height
• Watch form displacement
• Level top for column connection

Consolidation

Proper vibration:

• Insert vibrator into concrete
• Don't touch forms or rebar
• Withdraw slowly
• Vibrate until bubbles stop
• Don't over-vibrate

Column Connections

Various methods:

• J-bolts set in wet concrete
• Dowels extended from footing
• Post bases set in wet concrete
• Drilled and epoxy after curing

For wood posts:

• Simpson-type post bases
• J-bolts with washers and nuts
• Hot-dipped galvanized for exterior

Anchor Bolt Placement

Critical details:

• Use template for multiple bolts
• Set while concrete wet
• Correct projection (typically 2-3 inches)
• Protect from damage during curing
• Verify alignment before concrete sets

Inadequate Depth

Causes:

• Not accounting for frost depth
• Not removing organic soil
• Insufficient bearing capacity

Consequences:

• Foundation settling
• Structural damage
• Expensive repairs

Poor Soil Conditions

Signs of trouble:

• Soft, muddy soil
• Organic material (topsoil, roots)
• Fill dirt that wasn't compacted
• High water table

Solutions:

• Remove poor soil
• Over-excavate and backfill with gravel
• Increase footing size
• Engage engineer

Improper Reinforcement

Common mistakes:

• Rebar too close to soil (corrosion)
• Rebar not supported (sags to bottom)
• Insufficient reinforcement
• Wrong bar size or spacing

Consider professional help for:

• Building foundation footings
• Poor soil conditions
• Heavy structural loads
• Engineering requirements
• Unusual site conditions
• Large or complex projects

How much concrete for a standard deck footing?

For a typical 16×16×8 inch footing:

• Volume: 1.33 × 1.33 × 0.67 = 1.18 cubic feet
• Cubic yards: 0.044 cubic yards
• 80lb bags: 2 bags per footing
• For 6 footings: 12 bags

Do small footings need rebar?

• Code may not require for very small footings
• Recommended for durability
• Inexpensive insurance
• Good practice to always include

What's the minimum footing depth?

At minimum:

• Below frost line (varies by location)
• On undisturbed soil
• Remove all organic material
• Compact bearing surface

Can I pour footings in winter?

Possible with precautions:

• Excavate before ground freezes
• Protect excavation from snow
• Use concrete with accelerators
• Cover and insulate after pouring
• Wait longer before building on

Should footings be connected?

For decks and similar structures:

• Not typically required
• May help with stability
• Continuous footing may be required by code
• Follow design requirements

Accurate concrete calculation ensures your footing pour goes smoothly. Use our footing calculator to determine your needs, and always verify sizing and depth requirements with local building codes and a qualified professional when in doubt.

Remember: Footings are the foundation of your project—literally. Take the time to do them right, and your structure will serve you well for decades.