How Much Concrete for a Deck Footing? Bags per Hole

How much concrete for a deck footing? A 10-inch round tube form filled 42 inches deep holds about 1.9 cubic feet, roughly four 80-pound bags. A 12-inch tube at the same depth holds about 2.75 cubic feet, about five bags. Your footing size and depth come from your deck plans, local code and frost depth; once you have them, the math is simple.

Concrete calculator (post holes) →

Cubic feet per foot of depth

A round footing is a cylinder: volume = 3.1416 × (diameter ÷ 2)² × depth. Per foot of depth:

Tube diameter	ft³ per foot	36 in deep	42 in deep	48 in deep
8 in	0.35	1.05 ft³ · 2 / 3	1.22 ft³ · 3 / 3	1.40 ft³ · 3 / 4
10 in	0.55	1.64 ft³ · 3 / 4	1.91 ft³ · 4 / 5	2.18 ft³ · 4 / 5
12 in	0.79	2.36 ft³ · 4 / 6	2.75 ft³ · 5 / 7	3.14 ft³ · 6 / 7
16 in	1.40	4.19 ft³ · 7 / 10	4.89 ft³ · 9 / 11	5.59 ft³ · 10 / 13

Bag counts are shown as 80 lb / 60 lb bags per footing, rounded up, using Quikrete's yields of about 0.60 and 0.45 cubic feet (data sheet). They count a completely full column with no post embedded.

Footings with a wider base

Many deck footings are not straight tubes. A tube may sit on a wider square pad or a bell-shaped plastic footing form that spreads the load over more soil. Figure those in two parts: the pad or bell volume (from the form maker's listed volume, or length × width × thickness for a square pad) plus the tube above it. A 24 × 24 inch pad 8 inches thick adds about 2.7 cubic feet, roughly five more 80-pound bags.

Footing size and depth come from code and plans

Footing size depends on the load each post carries and the soil's bearing capacity. Many U.S. jurisdictions use the International Residential Code, which includes deck footing size tables, and many require the bottom of the footing to be below the local frost depth. Building departments often publish deck guides with typical footing details. Use your approved plans or local guidance rather than a rule of thumb, and expect an inspection before the pour.

Ordering for a whole deck

Multiply bags per footing by the number of footings, then add a few spare bags. Ten 12-inch footings 42 inches deep need about 27.5 cubic feet, roughly 46 to 50 bags of 80-pound mix, or about 1 cubic yard. At that size, a ready-mix truck or mixing trailer can be easier than bags; see bags per yard.

Tips for the pour

Brace tube forms so they stay plumb and do not float or shift as you fill them.
Rod or tap the tube as you fill to remove air pockets.
Set post bases or anchors while the concrete is wet, in the positions on your plan.
Slope the top slightly so water runs off.

For fence posts instead of deck footings, see bags of concrete per fence post, or use the concrete calculator for any hole.

Questions people ask

How many bags of concrete for a 12 inch deck footing?

A 12-inch tube filled 42 inches deep holds about 2.75 cubic feet, which is about five 80-pound bags or seven 60-pound bags, based on Quikrete yields.

How much concrete is in a 10 inch sonotube per foot?

About 0.55 cubic feet per foot of depth, or roughly one 80-pound bag for every 13 inches of depth.

How deep should deck footings be?

Deep enough to meet your local code, which often means below the frost depth. Your building department or approved plans set the depth.

Do I need a wider base under a deck footing?

Many designs use a wider pad or bell-shaped form to spread the load. Footing size depends on post load and soil, so follow your plans or local code tables.

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