Concrete Footing Calculator
Calculate concrete volume for footings, foundations, and piers
Enter Your Footing Dimensions
Perimeter or total linear feet
Typically 12-24 inches
Minimum 6-8 inches
Ready-mix: $120-200/yd³
Quick Answer
A standard residential footing is typically 16-24 inches wide and 8-12 inches deep. For a 100 linear foot foundation, you'll need approximately 3-5 cubic yards of concrete. Always check local building codes for frost line depth and footing size requirements in your area.
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Types of Footings Explained
Continuous/Strip Footings
Run along the entire length of a foundation wall.
- • Most common type
- • Supports foundation walls
- • Distributes load evenly
- • Width: 2× wall thickness
Pad/Spread Footings
Individual footings for columns or posts.
- • Isolated support points
- • Column/beam support
- • Square or rectangular
- • Sized for point loads
Pier/Circular Footings
Round holes filled with concrete.
- • Deck posts
- • Fence posts
- • Light pole bases
- • Easy to form
Footing Sizing Guidelines
| Application | Min. Width | Min. Depth |
|---|---|---|
| 1-Story House | 12" | 6" |
| 2-Story House | 15" | 6" |
| 3-Story House | 18" | 8" |
| Garage/Shed | 12" | 6" |
| Deck Post | 10-12" dia | Below frost |
| Fence Post | 8-10" dia | 1/3 post length |
* Always check local building codes. Soil conditions may require larger footings.
Rebar Reinforcement
Standard Reinforcement Pattern
- •2 horizontal bars (#4 or #5 rebar) placed 3" from bottom
- •Vertical dowels every 4 feet to tie into wall above
- •Overlap splices minimum 40 bar diameters (20" for #4)
- •Support chairs to hold rebar off ground
Rebar Size Reference
| Size | Diameter | Weight |
|---|---|---|
| #3 | 3/8" | 0.376 lb/ft |
| #4 | 1/2" | 0.668 lb/ft |
| #5 | 5/8" | 1.043 lb/ft |
| #6 | 3/4" | 1.502 lb/ft |
Pro Tip: Concrete Cover
Maintain minimum 3" concrete cover between rebar and soil for footings poured against earth. This protects the steel from moisture and corrosion over time.
Pouring and Curing Tips
- 1.Compact the base - Use gravel and compact thoroughly before pouring.
- 2.Check forms - Ensure forms are level, plumb, and properly braced.
- 3.Pour continuously - Avoid cold joints by pouring the entire footing at once.
- 4.Vibrate or rod - Remove air pockets by working the concrete.
- 5.Level the top - Strike off to create a flat, level surface for the foundation.
- 6.Cure properly - Keep moist for 7 days; don't load for 28 days.
Frequently Asked Questions
How deep should concrete footings be?
Footings should extend below the frost line in your area, typically 12-48 inches depending on location. For most residential construction, footings are at least 12 inches deep and extend below frost depth. Check local building codes for specific requirements.
How wide should a footing be?
A general rule is that footings should be twice as wide as the wall they support. For an 8-inch block wall, use a 16-inch wide footing. For load-bearing walls supporting multiple stories, footings may need to be wider based on soil bearing capacity.
Do I need rebar in concrete footings?
Yes, rebar reinforcement is recommended for most footings. Typically, two #4 or #5 rebar are placed horizontally near the bottom of the footing. Vertical dowels are used to connect the footing to the foundation wall above. This provides tensile strength the concrete lacks.
How many bags of concrete do I need for footings?
An 80-pound bag of concrete mix yields about 0.6 cubic feet. For example, a 2ft x 2ft x 1ft footing requires about 4 cubic feet or approximately 7 bags of 80lb concrete. For projects over 1 cubic yard, ready-mix delivery is more economical.
What is the minimum concrete strength for footings?
Minimum concrete strength for residential footings is typically 2,500 PSI, though 3,000-4,000 PSI is commonly specified for better durability. Commercial and industrial applications may require higher strengths. Check local building codes for specific requirements.
Can I pour footings in cold weather?
Concrete should not be poured when temperatures are below 40°F or expected to drop below freezing within 24 hours. Cold weather slows curing and can cause the concrete to freeze before setting, resulting in weak, crumbly footings.
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Dr. Snezana Lawrence
Mathematical Historian | PhD from Yale
Dr. Lawrence is a published mathematical historian with a PhD from Yale University. She ensures mathematical precision and accuracy in all our calculations, conversions, and academic score calculators. Her expertise spans computational mathematics and educational assessment.
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