Concrete Estimator - Tube
Find the concrete volume needed for round Sonotube-style footing forms, in bags or cubic yards.
📖 What is the Concrete Estimator - Tube?
The Concrete Estimator - Tube finds the volume of concrete needed to fill round, Sonotube-style cardboard footing forms, then converts it into cubic yards and premixed bag counts. These round forms are the standard method for pouring isolated round footings and piers for decks, fences, carports, and light structures across the US.
A Sonotube (the best-known brand name for this type of form) is a straight-sided cardboard cylinder, set into an augered or hand-dug hole and filled with concrete to create a clean, uniform round footing below grade. Because the tube is a true cylinder, its concrete volume follows the same pi r squared h formula used for any cylinder, with the tube's fill depth usually corresponding to the required frost-line depth rather than the full above-ground post height.
Footing tubes are almost always installed in matching sets, for example four corner footings for a deck or a run of fence post footings, so this calculator includes a quantity field to size the whole set in one calculation. It reports both cubic yards, the unit ready-mix trucks are ordered by, and premixed bag counts for smaller jobs where a truck delivery is not practical.
For the finished column or post that sits above a tube footing, see the companion Concrete Column Calculator, which covers both round and rectangular above-grade columns.
📐 Formula
📖 How to Use This Calculator
Steps
💡 Example Calculations
Example 1 - Four 12 inch deck footings
Example 2 - Six small fence post footings
Example 3 - One large 18 inch pier
❓ Frequently Asked Questions
🔗 Related Calculators
How do I calculate concrete for a Sonotube footing?
Use Volume = pi x radius squared x depth, where the radius is half the tube's diameter. A 12 inch diameter tube filled 4 feet deep has a radius of 0.5 feet, so the volume is pi x 0.5 squared x 4 = 3.14 cubic feet per tube.
What diameter Sonotube should I use for a deck footing?
Residential deck footings commonly use 8 to 12 inch diameter tubes, sized according to the deck's load and your local building code. Larger structures or poor soil conditions may require 16 inches or more; always confirm sizing against your local code or an engineer.
How deep should a concrete footing tube be filled?
Footing depth is typically set to your local frost line depth, which ranges from under 12 inches in warm climates to 4 feet or more in cold northern regions, so the footing sits below the depth at which the ground freezes and heaves. Check your local building department for the required depth.
How much concrete do I need for 4 deck footings?
For 4 footings using a 12 inch diameter tube filled 4 feet deep, each footing needs about 3.14 cubic feet, for a total of 12.57 cubic feet, or about 0.47 cubic yards, roughly 28 bags of 60 lb concrete.
Can I use this calculator for fence post footings?
Yes. Fence post footings are usually smaller diameter (8 to 10 inches) and shallower than deck footings, but use the exact same cylinder formula. Enter your tube diameter, footing depth, and number of posts.
What is the difference between a Sonotube and a post hole?
A Sonotube is a cardboard concrete form that creates a clean, straight-sided cylindrical footing, typically set inside a larger hand-dug or augered hole. This calculator sizes the concrete needed to fill the tube itself; use the Hole Volume Calculator if you need to estimate backfill or excavated soil around the outside of the tube.
How many bags of concrete fill one Sonotube footing?
Divide the tube's volume in cubic feet by the bag yield. A 12 inch diameter, 4 foot deep tube (3.14 cubic feet) needs about 7 bags of 60 lb concrete (3.14 divided by 0.45) or about 6 bags of 80 lb concrete.
Should I include the above-grade post height in the tube depth?
No, keep the below-grade footing depth and any above-grade column or post pour separate. This tool covers the round footing volume itself; size a separate round or rectangular column poured above it with the Concrete Column Calculator, if the design has both.
How do I convert Sonotube footing volume to cubic yards for ready-mix?
Divide the total cubic foot volume by 27. Twelve footings of 12 inch diameter, 4 feet deep total 37.7 cubic feet, which is 37.7 divided by 27, or about 1.4 cubic yards, close to a small ready-mix truck's minimum load.
What is a typical tube diameter to depth ratio for stability?
There is no fixed ratio; footing sizing depends on the load the footing carries and the local soil bearing capacity, not the tube's proportions alone. A structural engineer or your local building code table (often keyed to deck size and beam span) should set both diameter and depth for load-bearing footings.