Concrete Footing Size Guide (Depth, Width, and Sonotube Basics)
Last updated: February 2026
Concrete footing size depends on load requirements, soil type, and local building codes. Most residential footings are 12–24 inches wide and extend below frost depth, typically 12–48 inches depending on climate.
Use this guide to understand standard footing widths, depths, and reinforcement requirements before calculating volume with the concrete footing calculator.
Quick answer
- Footings should extend below local frost depth.
- Typical diameters are 12–18 inches for deck posts.
- Upsize for heavy loads or weak soils.
- Local code and soil conditions control final size.
Jump to
Common Residential Footing Sizes
| Structure Type | Typical Width | Typical Depth |
|---|---|---|
| Deck Footing | 12–16 in | Below frost line |
| Shed | 12–18 in | 12–24 in |
| Garage | 16–24 in | Below frost line |
| Load-Bearing Wall | 16–24 in | Per engineer/code |
What a footing does
Footings distribute structural loads into the soil so posts and columns do not settle. The stronger the soil, the smaller the footing can be. Weak or expansive soils require larger footings.
Depth guidance
Footings should extend below local frost depth and bear on undisturbed soil. Check local frost depth tables or building code before you dig.
Rule of thumb
If frost depth is 36 inches, plan on at least 42–48 inches of total depth to reach stable soil.
Diameter/width guidance by project
- Deck posts: 12–18 inch sonotubes are common.
- Pergolas: 12–16 inches depending on load and height.
- Small sheds: 16–24 inches if soil is soft or loads are higher.
Use the pier volume tool to convert tube sizes into yards.
Soil notes
Soft, sandy, or expansive soils require larger footings. If you can’t verify soil strength, upsize the footing or consult a pro.
Reinforcement basics
Small footings may not require rebar, but adding a vertical bar or small cage helps resist cracking and post movement.
Example
An 8-inch sonotube footing that is 48 inches deep is about 0.5 cubic feet (roughly 0.02 yd³). That is about 1 bag of 80-lb mix, plus waste.
Common mistakes
- Stopping above frost depth or soft soil.
- Undersizing diameter for heavier loads.
- Skipping base prep or compaction.
When to hire a pro
Hire a pro or engineer for large decks, retaining walls, or questionable soils. Code compliance varies widely by region.
Footing Size FAQs
How wide should a concrete footing be?
Footing width depends on load and soil capacity but is often twice the wall thickness.
How deep should footings go?
Footings must extend below the frost line in cold climates.
Do footings require rebar?
Most structural footings use reinforcement to prevent cracking and settlement.