Question 1

What is the difference between strip, pad, and pier footings?

Accepted Answer

Strip footings (also called continuous footings) run under walls to spread the load along their length. Pad footings sit under individual point loads like columns or posts. Pier footings are cylindrical concrete columns that transfer loads down to firmer soil — commonly used for decks, porches, and elevated structures.

Question 2

How deep should concrete footings be?

Accepted Answer

Footing depth depends on your local frost line and soil conditions. In cold climates, footings must extend below the frost line to prevent heaving — this ranges from 12 inches in mild climates to 48+ inches in colder northern regions. In frost-free areas, a minimum of 12 inches below grade is common for residential footings. Always check your local building code.

Question 3

How much concrete do I need for deck footings?

Accepted Answer

A typical deck pier footing uses a tube form 10–12 inches in diameter and 36–48 inches deep. A 10-inch diameter, 42-inch deep pier requires approximately 0.019 cubic yards (0.51 cubic feet) of concrete — about half an 80 lb bag. A 12-inch diameter, 42-inch deep pier needs approximately 0.027 cubic yards (0.73 cubic feet) — roughly one 80 lb bag. Most decks need 4–12 footings depending on size.

Question 4

How many bags of concrete per footing?

Accepted Answer

For a standard 10-inch diameter, 36-inch deep deck footing: approximately 1 bag of 80 lb concrete. For a 12-inch diameter, 42-inch deep footing: 1–2 bags of 80 lb. One 80 lb bag of premix concrete yields approximately 0.60 cubic feet (0.022 cubic yards). Use the calculator above to get exact bag counts for your specific footing dimensions.

Question 5

Should I use ready-mix or bagged concrete for footings?

Accepted Answer

For small projects with fewer than 6–8 footings, bagged concrete mixed on site is usually more practical. For large projects — many footings, large strip footings, or foundation work — ready-mix delivery is faster and more consistent. The break-even point is roughly 0.5–1 cubic yard (half a cubic yard is about 13 bags of 80 lb concrete).

Question 6

Can I use this calculator for engineering design?

Accepted Answer

No — this tool estimates concrete quantities only. Footing size, depth, and reinforcement requirements must be determined by a structural engineer or by following your local building code. Never use quantity estimates for structural design decisions.

Footing type	Typical size	Volume (per unit)	80 lb bags (per unit)
Deck pier (10" dia.)	10" dia. × 36" deep	0.016 yd³	~1 bag
Deck pier (12" dia.)	12" dia. × 42" deep	0.027 yd³	~2 bags
Fence post footing	10" dia. × 30" deep	0.014 yd³	~1 bag
Strip footing (house)	24" wide × 8" deep × 20 ft	0.99 yd³	~46 bags (use ready-mix)
Pad footing (post)	18" × 18" × 12" deep	0.083 yd³	~4 bags
Pad footing (garage)	24" × 24" × 12" deep	0.148 yd³	~7 bags

Region / climate	Frost line depth	Min. footing depth
Southern US (FL, TX, LA)	0–6 inches	12 inches below grade
Mid-Atlantic (VA, NC, TN)	8–18 inches	18–24 inches below grade
Midwest (OH, IL, MO)	24–36 inches	36–42 inches below grade
Northern US (MN, WI, MI)	42–60 inches	48–66 inches below grade
Mountain / high elevation	48–72 inches	Check local code

Volume	80 lb bags equiv.	Recommendation
Under 0.25 yd³	Under 12 bags	Bagged concrete — practical for small jobs
0.25–0.75 yd³	12–35 bags	Either — depends on site access and timeline
0.75–2 yd³	35–90 bags	Ready-mix strongly recommended
Over 2 yd³	Over 90 bags	Ready-mix only — bags impractical

Concrete Footing Calculator

Need a concrete contractor for this project?

Concrete Footing Calculator — Strip, Pad & Deck Pier Guide

Common Footing Sizes — Reference Table

How Deep Should Footings Be?

Bags vs Ready-Mix — When to Switch

Formulas Used

Frequently Asked Questions

Concrete Footing Planning Checklist

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