Concrete Footing Calculator
Quick Presets
Round Footing Concrete Volume
Cubic feet per footing by diameter and depth.
| Diameter | 36" Deep | 42" Deep | 48" Deep |
|---|---|---|---|
| 8" | 0.12 | 0.14 | 0.17 |
| 10" | 0.18 | 0.21 | 0.27 |
| 12" | 0.26 | 0.33 | 0.39 |
| 14" | 0.36 | 0.45 | 0.53 |
| 16" | 0.47 | 0.58 | 0.70 |
| 18" | 0.59 | 0.74 | 0.88 |
| 24" | 1.05 | 1.31 | 1.57 |
How We Calculate This
This concrete footing calculator uses established formulas and industry-standard data to provide accurate estimates.
- Enter your specific values into the calculator fields above
- Our algorithm applies the relevant formulas using your inputs
- Results are calculated instantly in your browser — nothing is sent to a server
- Review the detailed breakdown to understand how each factor affects your result
These calculations are estimates based on standard formulas. For critical decisions, always consult a qualified professional.
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Footings support structures by distributing weight into the ground. Calculating the right amount of concrete depends on the footing shape, size, and quantity.
The basic rule:
- Round footings (piers): π × (diameter/2)² × depth. Convert all measurements to feet first
- Rectangular footings: length × width × depth. Typical wall footings are twice the wall width
- Footings must extend below the frost line — check your local building code for the required depth
For deck piers and post footings, round Sonotube forms are most common. For wall footings and strip footings, rectangular forms are standard. Always add 10% extra concrete for waste and spillage.
When Would You Use This Calculator?
This concrete footing calculator is designed for anyone who needs quick, reliable estimates without complex spreadsheets or professional consultations.
- When you need a quick estimate before committing to a purchase or project
- When comparing different options or scenarios side by side
- When planning a budget and need to understand potential costs
- When you want to verify a quote or estimate you've received from a professional
- When teaching or learning about the concepts behind these calculations
Frequently Asked Questions
How deep should footings be?
Footings must extend below the frost line, which ranges from 12 inches in southern states to 48+ inches in northern states. Check your local building code. Typical depths: deck footings 36-48 inches, fence posts 24-36 inches, house footings per engineer specs.
What size footing do I need for a deck?
Most deck footings use 12-inch diameter Sonotube forms set 42 inches deep. For heavy loads or tall decks, 16-inch or 18-inch diameter may be required. Check your local building code — most require a permit and specify minimum footing sizes for decks.
How much concrete for a fence post hole?
A typical fence post hole (8 inches diameter, 36 inches deep) uses about 0.3 cubic feet of concrete — roughly one 50-lb bag per post. For a 6-foot privacy fence, you need a post every 6-8 feet, so a 100-foot fence needs about 13-17 posts.
Can I mix my own concrete for footings?
For a few small footings, bagged concrete mix is practical. For larger jobs (over 1 cubic yard), ordering ready-mix is faster, stronger, and often cheaper. One 80-lb bag yields about 0.6 cubic feet of concrete.
Do footings need rebar?
Most building codes require at least 2 pieces of #4 rebar in wall footings and 1 piece of rebar extending up from pier footings into the post bracket. Rebar prevents cracking and ties the footing to the structure above. Always follow your local code.
What is the difference between a footing and a pier?
A footing is a wider concrete base that spreads the load over more soil — typically used under walls and foundations. A pier is a round or square column of concrete (often formed with a Sonotube) that carries point loads, like deck posts. Many structures use both: a footing at the bottom with a pier extending up.