How many bags of concrete do I need for a 12-inch Sonotube?
A 12 in tube that is 48 in deep holds 3.14 cu ft, which is 6 bags of 80-lb mix. At 36 in deep it holds 2.36 cu ft and takes 4 bags. Add the allowance if you want a few bags in reserve.
Sonotube Concrete Calculator: Bags and Yards per Tube
Enter the diameter and depth of your round footings and how many you pour. The calculator returns the concrete for all tubes in cubic yards and in 80-lb bags, with an allowance, and compares bags with a ready-mix delivery.
1. Material Grade & Project Dimensions
Area: 4.7 sq ft (0.44 m²)Net Vol: 0.70 cu yd (0.53 m³)
2. Material Takeoff, Blueprint & Cost
Total Concrete Volume (incl. waste)
0.77 cu yd (0.59 m³)
20.7 cu ft · 3,069 lbs (1.53 US tons)
80-lb Concrete Bags (0.60 ft³)
35 bags
0.8 pallets (@ 42 bags/pallet)
60-lb or 40-lb Bag Option
47 × 60-lb
or 70 × 40-lb (0.30 cu ft)
Rebar Grid (#4 @ 18" O.C.)
7 lin ft
1 × 20-ft bars recommended
4" Compacted Gravel Sub-Base
0.08 US tons
Crushed stone base under slab
Cost Break-Even: Ready-Mix Truck vs. 80-lb Bags
Bags save $14
Ready-Mix Delivery (0.77 cu yd + $140 short-load fee)
$188
35 × 80-lb Pre-Mix Bags
$174
Show Step-by-Step Formula & Takeoff Math
Net Area = 4.71 sq ft (0.44 m²)
Net Volume = 18.85 cu ft ÷ 27 = 0.70 cu yd
Total Volume (+10% waste) = 20.73 cu ft = 0.77 cu yd (0.59 m³)
80-lb Bags = ceil(20.73 ÷ 0.60) = 35 bags
How much concrete a Sonotube takes
A round form tube, often sold under the brand name Sonotube, is a cylinder, so its volume is π × radius² × depth. The calculator uses a circle zone for this: the diameter goes in the first field in feet and the depth in inches, and the count field multiplies the result by the number of tubes. A 12 in tube holds 0.79 cu ft of concrete per foot of depth.
Example: six 12 in tubes that are 48 in deep need 18.85 cu ft net, or 20.73 cu ft with the 10% allowance. That is 0.77 cu yd or 35 bags of 80-lb mix. Each single tube takes 6 bags.
The calculator fills the tube completely and does not subtract the post or rebar. It also has no flared (belled) base: add a second zone for the base if you pour one. Enter inch diameters as decimal feet, for example 0.83 ft for a 10 in tube; the chart below lists the value to type for each size.
Concrete per Sonotube by diameter and depth (no allowance)
| Tube diameter | Enter in calculator | 36 in deep | 48 in deep |
|---|---|---|---|
| 8 in | 0.67 ft | 1.06 cu ft · 2 bags | 1.41 cu ft · 3 bags |
| 10 in | 0.83 ft | 1.62 cu ft · 3 bags | 2.16 cu ft · 4 bags |
| 12 in | 1 ft | 2.36 cu ft · 4 bags | 3.14 cu ft · 6 bags |
| 16 in | 1.33 ft | 4.17 cu ft · 7 bags | 5.56 cu ft · 10 bags |
| 18 in | 1.5 ft | 5.30 cu ft · 9 bags | 7.07 cu ft · 12 bags |
| 24 in | 2 ft | 9.42 cu ft · 16 bags | 12.57 cu ft · 21 bags |
Frequently Asked Questions & Field Guide
How do I calculate the volume of a round footing?
Use the cylinder formula, π × radius² × depth, with the radius in feet to get cubic feet. For a 12 in tube the radius is 0.5 ft, so each foot of depth holds 0.79 cu ft. Divide by 27 for cubic yards.
How much concrete do six footings need?
Six 12 in × 48 in tubes need 0.77 cu yd with a 10% allowance, which is 35 bags of 80-lb mix costing $226 at $6.45 a bag. Ready-mix would come to $305 at the default prices, including the short-load fee, because the volume is far below 4 cu yd.
Does the calculator include the bell at the bottom of a footing?
No. It models a straight cylinder only. If your footing has a flared base, add a second circle zone with the diameter and thickness of the base and the calculator adds both volumes.
Related calculators & tools
Concrete Slab & Bag Calculator
Concrete calculator for slabs, footings and post holes: cubic yards, 80-lb and 60-lb bag counts, rebar and ready-mix truck cost.
Fence Post Concrete Calculator
Bags of concrete per post hole and for a whole fence line.
Cubic Yards to Tons Converter
Convert cubic yards, cubic feet and cubic meters to tons for 24 materials, with a density table.