Sonotube Concrete Calculator
Calculate the concrete needed to fill a round Sonotube form or pier footing, per tube and for the whole job, in cubic feet, cubic yards, and bags.
Reviewed by the ToolNestr Editorial Team — July 2026
How the Sonotube calculator works
A Sonotube is a waxed cardboard tube used as a one-time form for round concrete piers, deck footings, and column bases. Because the form is a simple cylinder, the concrete inside it is just the volume of that cylinder — pi times the radius squared times the height.
The one trick is units. The diameter is measured in inches but the depth in feet, so the calculator converts the diameter to a radius in feet by dividing by 24 (halve it to a radius, then divide by 12 to change inches to feet). It then squares that radius, multiplies by pi and the depth to get cubic feet, multiplies by the number of tubes, and adds your waste allowance. Cubic yards come from dividing by 27, and bag counts from the standard yields of 0.6 cubic feet for an 80 lb bag and 0.45 for a 60 lb bag.
This follows the standard cylinder-volume geometry used in ACI 318 concrete work. The result covers the straight tube only — if your footing flares out to a wider bell or sits on a square pad, estimate that base separately and add it in.
Enter the tube size
Use the tube diameter in inches (6, 8, 10, 12 are common) and the pour depth in feet.
Count the tubes
Enter how many identical tubes you are pouring so the total scales to the whole job.
Add waste
Add 5-10% for spillage and an uneven hole bottom, then round bags up.
The formula explained
Volume per tube
V = π × (D⁄24)² × H. A 12-inch tube 4 ft deep: π × (12⁄24)² × 4 = π × 0.25 × 4 = 3.14 ft³.
Total volume
Total = V × tubes × (1 + waste). Four such tubes with 10% waste: 3.14 × 4 × 1.10 = 13.8 ft³, or 0.51 cubic yards.
Bag count
Bags = total ÷ yield. Using 80 lb bags (0.6 ft³): 13.8 ÷ 0.6 = 23 bags.
Worked example
Six 8-inch tubes for a deck, each 3.5 ft deep, with 5% waste.
Where round tube footings are used
Deck and porch footings
Tube footings carry deck posts down to solid, below-frost soil. Most residential decks use 8 to 12 inch tubes spaced along the beam lines.
Pole barns and pergolas
Posts for pergolas, carports, and pole barns are set in tube footings so the column base stays dry and locked against uplift and frost.
Sign and fence posts
Large gate posts, mailbox clusters, and sign bases use small-diameter tubes to set a clean, straight concrete pier without a messy dug hole.
Cabin and shed piers
Small buildings on a pier foundation sit on a grid of tube footings instead of a full slab, which saves concrete on sloped or remote sites.
Tips for pouring tube footings
Go below the frost line
The whole point of a deep pier is to reach undisturbed soil below where the ground freezes. A footing that stops short of the frost line will heave in winter and rack the structure above it.
Brace the tube before you pour
Wet concrete is heavy and can float or tilt an unbraced tube. Backfill and brace each tube plumb, and pour in lifts so the form does not blow out at the bottom.
Order by the bag or the yard
A handful of small tubes is cheapest with bagged mix. Once your total passes roughly a cubic yard, compare the bag count against a short-load ready-mix delivery, which may cost less and pour faster.
Real-world context
A typical raised deck shows this calculator's most common use: eight 10-inch tube footings at 4 ft deep (below a northern frost line) need 8 × π × (10/24)² × 4 ≈ 8 × 2.18 = 17.4 cubic feet total, about 29 bags of 80 lb mix — a job most homeowners handle with a wheelbarrow mixer rather than ordering ready-mix.
A pole barn or carport post footing runs larger: a single 16-inch tube 5 ft deep holds π × (16/24)² × 5 ≈ 6.98 cubic feet per post — for a 6-post structure, that's roughly 41.9 cubic feet total, about 1.55 cubic yards, right at the point where comparing a short-load ready-mix delivery against 70 bags of mix actually matters for cost.
At the small end, a mailbox post or gate post pier might use a single 8-inch tube 3 ft deep — π × (8/24)² × 3 ≈ 1.05 cubic feet, easily covered by two 80 lb bags with room to spare, which is why single-tube jobs rarely justify anything beyond bagged concrete.
Common misconceptions
"A deeper footing is only about reaching solid ground." Frost depth is the real driver. Even soil that feels solid year-round will heave when the water in it freezes and expands; a footing that stops above the local frost line can be pushed upward each winter regardless of how firm the soil felt when you dug it.
"The tube diameter is the same as the hole diameter, so any size auger works." Not quite. The Sonotube itself has some wall thickness, and the surrounding hole needs to be dug slightly larger than the tube's outside diameter to actually fit it in and backfill around it — order the tube first, then match the auger or hole size to it.
Related calculators
Frequently asked questions
How much concrete do I need for a 12-inch Sonotube?
A 12-inch diameter tube holds about 0.79 cubic feet of concrete per foot of depth. At 4 feet deep that is about 3.14 cubic feet, or roughly six 80 lb bags once you add waste. Always round up to whole bags.
What is the formula for concrete in a round tube?
Volume in cubic feet = 3.14159 x (diameter in inches / 24)^2 x depth in feet. Dividing the diameter by 24 converts it to a radius in feet, and squaring it and multiplying by pi and the depth gives the cylinder volume.
How deep should a Sonotube footing be?
The bottom of the footing must sit below your local frost line so that freezing, expanding soil cannot heave it. Frost depth ranges from near zero in warm climates to 48 inches or more in cold regions. Check your local building department for the required depth.
Should I add a wider footing at the base?
Many pier footings have a bell or a separate square pad at the bottom to spread the load. This calculator sizes the straight tube only. Estimate the base pad separately as a slab or box and add it to the total.
Sources & references
This tool uses standard formulas and reference values from:
- • American Concrete Institute — ACI 318, Building Code Requirements for Structural Concrete. concrete.org
- • ICC — International Residential Code (IRC), span, footing and framing tables. codes.iccsafe.org
- • APA – The Engineered Wood Association, allowable span and load guidance.
Estimates for planning only. Span, load and code values vary by jurisdiction — verify against your local adopted code and a licensed engineer before building.