Question 1

How much concrete do I need for a footing?

Accepted Answer

For rectangular footings: length × width × depth (all in feet). For round footings: π × radius² × depth. Divide by 27 for cubic yards. A 12" diameter footing at 36" deep needs about 0.087 cubic yards.

Question 2

How do you calculate concrete for a round footing?

Accepted Answer

Use the formula: Volume = π × (diameter ÷ 2)² × depth. Convert diameter and depth from inches to feet first. For a 12" diameter, 36" deep footing: π × 0.5² × 3 = 2.36 cubic feet = 0.087 cubic yards.

Question 3

How deep should concrete footings be?

Accepted Answer

Footings must extend below the frost line, which varies by region: 0–6" in the Southern US, 36–48" in the Midwest and Northeast, and up to 60" in northern states. Check your local building codes.

Question 4

How many bags of concrete for a deck footing?

Accepted Answer

A typical 12" diameter, 36" deep deck footing needs about 2.36 cubic feet of concrete, which equals approximately 4 bags of 80 lb concrete or 6 bags of 60 lb.

Question 5

What size footing do I need for a deck post?

Accepted Answer

Most residential decks use 12" diameter footings extending 36–48" below grade. For larger decks or multi-story structures, 16" diameter or larger may be required. Always verify with local building codes.

Question 6

How much concrete for a sonotube?

Accepted Answer

It depends on the tube diameter and depth. A 12" sonotube at 48" deep needs about 3.14 cubic feet (0.12 cubic yards). Our calculator handles sonotube calculations with the cylindrical shape option.

Question 7

Do I need rebar in concrete footings?

Accepted Answer

Building codes often require rebar in footings, especially for structural loads. Rebar reduces cracking and improves tensile strength. It does not significantly change the volume of concrete needed.

Question 8

How many footings do I need for a deck?

Accepted Answer

Deck footing count depends on the deck size and joist span. A typical rule is one footing every 6–8 feet along each beam. A 12×16 deck might need 6–9 footings. Consult your local building department for requirements.

Question 9

Should I use bags or ready-mix for footings?

Accepted Answer

Most footing projects use 0.5–3 cubic yards total. Under 1 cubic yard, bags are practical and cost-effective. Over 1 cubic yard, ready-mix delivery saves significant time and effort.

Type	Shape	Size	Per Footing
Deck post	Round	12" dia × 36"	0.07 yd³
Deck post	Round	12" dia × 48"	0.10 yd³
Fence post	Round	8" dia × 24"	0.02 yd³
Pier/Sonotube	Round	14" dia × 48"	0.14 yd³
Wall footing	Rectangular	24"W × 12"D	0.07/lin ft
Column footing	Rectangular	24"×24"×12"	0.15 yd³

Concrete Footing Calculator

How to Calculate Concrete for Footings

Rectangular Footing Formula

Cylindrical (Round) Footing Formula

Footing Size Reference

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Concrete Footing Calculator — Frequently Asked Questions