Sonotube Calculator

Q: What formula does this sonotube calculator use?

It uses the cylinder volume formula: Volume = π × radius² × height . The radius is half the diameter. The calculator converts your inputs to inches, runs the formula, then shows results in cubic feet, cubic yards, and other units.

Q: What unit should I enter my sonotube diameter in?

You can use any unit you want. The calculator supports inches, feet, centimeters, meters, and yards . Just pick the matching unit from the dropdown next to the input field.

Q: What is the weight estimate based on?

The calculator uses 150 pounds per cubic foot , which is the standard weight of cured concrete. This gives you a good estimate of how heavy your finished footings will be. It shows the result in both pounds and kilograms.

Q: How many 80 lb bags of concrete fill a 12-inch sonotube that is 4 feet deep?

One 12-inch tube at 4 feet deep holds about 3.14 cubic feet of concrete. An 80 lb bag yields about 0.6 cubic feet. You need roughly 6 bags per tube with a 10% waste factor. Enter your numbers in the calculator to get an exact count.

Sonotube Calculator

Updated May 25, 2026 By Jehan Wadia

Introduction

A sonotube is a round cardboard form used to pour concrete footings and pillars. You set it in the ground, fill it with concrete, and let it cure to create a strong column. This sonotube calculator tells you exactly how much concrete you need. Enter the tube diameter, height, and how many tubes you have. It gives you the total volume in cubic feet, cubic yards, and other units. It also tells you how many bags of premixed concrete to buy. You can add rebar details and a waste factor for a more accurate estimate. Use this tool to save time, avoid waste, and get your concrete project right the first time.

How to Use Our Sonotube Calculator

Enter your tube size and quantity below. The calculator will tell you how much concrete you need in volume, weight, and number of bags.

Preset Diameter: Pick a common sonotube size from the dropdown list. This fills in the diameter for you.

Tube Diameter: Type in the width across your sonotube. Change the unit to inches, feet, centimeters, meters, or yards as needed.

Tube Height / Depth: Enter how tall or deep your sonotube is. This is the length of the tube going into the ground.

Quantity: Enter the total number of sonotubes you need to fill with concrete.

Number of Rebar Bars: If you are placing rebar inside the tube, enter how many bars. Leave it at 0 if you have no rebar. This adjusts the concrete volume so you get a more accurate result. You can also use our Rebar Calculator to plan the steel reinforcement for your project.

Rebar Diameter: Enter the thickness of each rebar bar. Common sizes are 0.5 inches for #4 rebar, 0.625 inches for #5, and 0.75 inches for #6.

Concrete Mix Mode: Choose "Standard Bags" to see how many 40, 50, 60, 80, or 90 lb bags you need. Choose "Custom Yield" if you use a bag size not on the list.

Waste Factor: Move the slider to set how much extra concrete to add for spills and overfill. A 10% waste factor is normal for most jobs.

Custom Bag Weight and Yield: If you picked Custom Yield mode, type in your bag weight and how many cubic feet of concrete one bag makes. This info is on the bag label.

Press Calculate to see your results. Press Reset to clear all fields and start over.

What Is a Sonotube and How Do You Calculate Concrete for It?

A Sonotube is a round cardboard tube used as a form for pouring concrete columns, posts, and footings. You place it in a hole in the ground, fill it with concrete, and let it harden. Once the concrete sets, the tube is peeled away or left to break down. Sonotubes are commonly used to build deck footings, fence posts, mailbox supports, and foundation piers. For broader concrete projects beyond tubes, our Concrete Calculator can help you estimate material for slabs, walls, and other shapes.

To figure out how much concrete you need for a Sonotube, you must know two things: the diameter (how wide the tube is) and the height or depth (how tall the tube is or how deep it goes in the ground). The calculator uses the formula for the volume of a cylinder: Volume = π × radius² × height. The radius is half the diameter. If you need to calculate the volume of other cylindrical shapes, our Cylinder Volume Calculator works with the same formula.

Common Sonotube Sizes

Sonotubes come in standard diameters ranging from 6 inches to 60 inches. The most popular sizes for residential work are 8, 10, and 12 inches. Deck footings typically use 10-inch or 12-inch tubes. Larger tubes like 24 inches or 36 inches are used for heavy structural columns. If you're building a deck, you may also need our Decking Calculator to estimate the lumber for the surface.

How Deep Should a Sonotube Go?

Your tube must go below the frost line in your area. The frost line is how deep the ground freezes in winter. If your footing is above the frost line, freezing soil can push it up and crack your structure. Frost lines range from 12 inches in warm climates to over 60 inches in cold regions. Check your local building code to find the exact depth required. You may need to dig out a significant amount of earth; our Excavation Calculator can help you estimate the volume of soil to remove.

Why Add a Waste Factor?

Concrete mix always has some waste. You spill a little, some sticks to the wheelbarrow, and tubes sometimes get overfilled. A waste factor of 10% is standard. This means you buy 10% more concrete than the exact calculated volume. It is always better to have a little extra than to run short in the middle of a pour.

Rebar in Sonotubes

Rebar is steel bar placed inside the tube before pouring concrete. It makes the footing much stronger. Most building codes require at least one or two bars of #4 or #5 rebar in each footing. Rebar takes up a small amount of space inside the tube, so the calculator can subtract that volume to give you a more accurate concrete estimate. For projects involving concrete slabs and footers, our Concrete Slab Calculator can assist with flat-pour estimates, and the Concrete Block Calculator is useful if you're combining block walls with poured footings.

Pre-Mixed Concrete Bags vs. Ready-Mix

For small jobs with a few tubes, pre-mixed bags from the hardware store work well. They come in 40, 50, 60, 80, and 90 pound sizes. For large projects with many tubes or wide diameters, ordering ready-mix concrete delivered by truck is faster and often cheaper. A general rule is that if you need more than one cubic yard total, ready-mix is worth considering. If you need to convert between volume units for ordering, our Cubic Yard Calculator and Cubic Feet Calculator make that easy. To estimate the weight of your pour, check out our Concrete Weight Calculator. And if your project also involves footings around a fence or retaining structure, our Fence Calculator and Retaining Wall Calculator can help plan those parts of the job.

Frequently asked questions

What formula does this sonotube calculator use?

It uses the cylinder volume formula: Volume = π × radius² × height. The radius is half the diameter. The calculator converts your inputs to inches, runs the formula, then shows results in cubic feet, cubic yards, and other units.

What unit should I enter my sonotube diameter in?

You can use any unit you want. The calculator supports inches, feet, centimeters, meters, and yards. Just pick the matching unit from the dropdown next to the input field.

How do I know what size sonotube I need?

The size depends on the load the footing must carry. For a standard residential deck, 10-inch or 12-inch tubes are most common. For heavier structures like large decks or porches, 14-inch to 24-inch tubes may be needed. Check your local building code or ask your building inspector for the required size.

How accurate is the bag estimate?

The bag estimate is very close to what you will need in practice. It uses the yield values printed on standard concrete bags. The waste factor slider adds extra to cover spills and overfill. With a 10% waste factor, most users find the estimate matches real-world use well.

What does the waste factor do?

The waste factor adds extra concrete to your estimate. It accounts for spillage, concrete left in the mixer, and slight overfilling of tubes. The default is 10%, which works for most jobs. You can slide it from 0% to 25% depending on your situation.

Does rebar really change how much concrete I need?

Yes, but only by a small amount. Rebar takes up space inside the tube, so you need slightly less concrete. For most residential footings with 2 or 3 bars, the difference is tiny. The calculator subtracts the rebar volume so you get a precise number.

What is the weight estimate based on?

The calculator uses 150 pounds per cubic foot, which is the standard weight of cured concrete. This gives you a good estimate of how heavy your finished footings will be. It shows the result in both pounds and kilograms.

When should I use Custom Yield mode instead of Standard Bags?

Use Custom Yield mode when your concrete bag is not one of the standard sizes (40, 50, 60, 80, or 90 lb). Enter the bag weight and the yield in cubic feet printed on the bag label. The calculator will then tell you how many of those bags you need.

Can I mix different sonotube sizes in one calculation?

No. This calculator handles one tube size at a time. If you have tubes of different diameters or heights, run the calculator once for each size. Then add the volumes together to get your total concrete need.

How many 80 lb bags of concrete fill a 12-inch sonotube that is 4 feet deep?

One 12-inch tube at 4 feet deep holds about 3.14 cubic feet of concrete. An 80 lb bag yields about 0.6 cubic feet. You need roughly 6 bags per tube with a 10% waste factor. Enter your numbers in the calculator to get an exact count.

What does the quick reference table show?

The table shows the concrete volume in cubic feet for common sonotube sizes and heights. It covers diameters from 6 inches to 48 inches and heights from 2 feet to 8 feet. Your current selection is highlighted in green so you can compare it to other sizes.

Can I use this calculator for round concrete columns that are not sonotubes?

Yes. Any round concrete form works the same way. Enter the diameter and height of your form and the calculator will give you the correct volume. It does not matter if the form is cardboard, plastic, or metal.

Should I round up or round down when buying concrete bags?

Always round up. The calculator already rounds up the bag count for you. Running out of concrete during a pour is a big problem because the first batch starts to set before you can get more. It is always better to have one extra bag.

What is the difference between cubic feet and cubic yards?

There are 27 cubic feet in one cubic yard. Cubic feet are better for small jobs and bag counts. Cubic yards are used when ordering ready-mix concrete from a truck. The calculator shows both so you can use whichever you need.

How do I measure the diameter of my sonotube?

Measure straight across the top opening from one inside edge to the other. This gives you the inside diameter, which is what matters for concrete volume. The size printed on the tube label is usually the inside diameter.