Sonotube Calculator

1. Pick the tube diameter from the standard sizes, or choose Custom diameter and type the inside diameter in inches.
2. Enter the tube height in feet, counting the full height that will be filled, including the part buried in the hole.
3. Set the number of tubes of that size and a waste allowance; the default is 10 percent.
4. Pick a bag size, then read the cubic yards, the total bags and the bags for each tube.

If your piers use two or more tube sizes, run the calculator once for each size and add the totals. Here is what each result line means:

A Sonotube calculator estimates how much concrete it takes to fill round cardboard concrete form tubes. Sonotube is the brand name Sonoco uses for its fiber form tubes, and the name is often used loosely for any Sonotube-style cardboard form. The tubes are set in a hole or on a footing, braced plumb and filled with concrete to make round piers for decks, porches, sheds, posts and similar small structures.

Because each tube is a simple cylinder, the volume depends only on its inside diameter and the height you fill. The catch is that the diameter is squared, so moving up one size adds more concrete than most people expect, and a job with many tubes adds up quickly. This tool totals every tube, adds waste and turns the result into cubic yards and bags.

If the bottom of your pier widens into a flared footing below the tube, the concrete bell pier calculator handles the bell shape. To decide between mixing bags and ordering a truck, the bagged vs ready-mix calculator compares the two.

A filled form tube is a cylinder. Its volume is the area of the circle, pi times the radius squared, multiplied by the height. The radius is half the diameter, and both have to be in feet before multiplying so the answer comes out in cubic feet.

1. Halve the tube diameter and divide by 12 to get the radius in feet. A 12 inch tube has a 0.5 ft radius.
2. Square the radius and multiply by pi for the cross-section area in square feet, which is also the cubic feet of concrete per foot of height.
3. Multiply by the tube height for one tube, then by the number of tubes, and add the waste percentage.
4. Divide by 27 for cubic yards, and divide the cubic feet by the bag yield for the number of bags, rounded up.

Sonoco publishes its own charts for these numbers. Its Builder’s Tube brochure lists 0.20, 0.35, 0.55 and 0.80 cubic feet per foot of height for 6, 8, 10 and 12 inch tubes, which sit at or just above the geometry values of 0.196, 0.349, 0.545 and 0.785. Its round form brochure lists cubic yards by height; at 10 feet a 12 inch column is 0.291 cubic yards and a 24 inch column 1.164, the same figures the cylinder formula gives (see the size table below).

Suppose you are setting 4 deck piers in 12 inch form tubes, each filled 4 feet high, with 10 percent waste, and you plan to mix 80 lb bags.

Calculation: the radius is 12 / 24 = 0.5 ft. The area is pi x 0.5 x 0.5 = 0.785 sq ft, so each foot of tube holds 0.785 cubic feet. One 4 foot tube is 0.785 x 4 = 3.14 cu ft. Four tubes are 12.566 cubic feet, and with 10 percent waste that is 12.566 x 1.10 = 13.82 cu ft. Dividing by 27 gives 0.51 cu yd. At 0.60 cubic feet per 80 lb bag, 13.82 / 0.60 = 23.04, which rounds up to 24 bags, or about 5.8 bags per tube.

The lesson: four modest piers already take two dozen heavy bags. Line up the bags, water and a mixer before you start, so each tube can be filled in one go.

This table gives the concrete in each common tube size from the cylinder formula, with no waste added. Multiply the per-foot figures by your tube height, then add your waste allowance.

The 10 foot column matches the cubic yard figures in Sonoco’s round form brochure for the same diameters. Sonoco’s Builder’s Tube chart rounds the bag counts for easy use, listing 1/3, 3/5, 1 and 1 1/3 eighty-pound bags per foot for 6, 8, 10 and 12 inch tubes, and 1/2, 4/5, 1 1/4 and 2 sixty-pound bags per foot. Those rounded figures sit at or above the exact values here, by up to about 15 percent for the 60 lb figures, which leaves some extra.

Tube Diameter

The radius is squared, so doubling the diameter quadruples the concrete. A 24 inch tube holds four times as much per foot as a 12 inch tube. Sonoco notes its Builder’s Tube sizes are nominal, so measure the inside diameter if the number matters.

Filled Height

Volume rises in step with height. Count the full height that will hold concrete, from the bottom of the hole or footing to the top of the tube, not just the part above grade.

Number of Tubes

Small errors repeat on every tube. A deck with a dozen piers multiplies any rounding or mismeasurement twelve times.

The Hole Below the Tube

If the tube sits above a wider hole or a cast footing, that concrete is extra. Estimate any footing separately and add it to the tube total.

Waste and Spillage

Concrete is lost to spills, the mixer drum and an uneven hole bottom. A waste allowance covers it so the last tube is not left short.

Sonoco sells several lines of round concrete forms. The sizes below are from its product literature; check the current range with your supplier, because stock varies.

The volume math is the same for every line: only the inside diameter and the filled height matter. For diameters above 24 inches, choose Custom diameter in the calculator and enter the size. For the weight of a finished pier, the concrete weight calculator converts the volume to pounds.

Deck and Porch Piers

Total the tubes for a deck or porch so you buy the right number of bags in one trip, or know whether a delivery makes more sense.

Shed, Pergola and Post Bases

Small round piers under a shed, pergola or carport can be totaled the same way, and the bags-per-tube line tells you how much to mix each time.

Comparing Tube Sizes

See how much more concrete a larger tube takes before you commit to a size. Going from 10 to 12 inch adds about 44 percent per foot.

Planning a Fast-setting Pour

For small posts set with fast-setting mix, pick the 50 lb fast-setting option. The fast-setting concrete calculator covers that product in more depth.

1. Using the Diameter as the Radius

The formula needs the radius, half the diameter. Using the full diameter gives four times the real volume.

2. Measuring Only the Part Above Ground

The buried part of the tube fills with concrete too. Count the whole filled height.

3. Forgetting the Footing Below the Tube

A tube set on a wider footing or flared base needs that concrete as well. Estimate it separately and add it in.

4. Rounding Bags per Tube Down

If one tube needs 5.8 bags, mixing 5 leaves it short. Round up per tube, or use the total bag count, which is already rounded up.

5. Treating the Estimate as a Design

Pier size, depth and spacing come from your plans, an engineer or the local code, not from this tool, which only sizes the concrete order.

The cylinder math is exact; the real answer depends on how closely the tube and hole match the numbers you enter.

Multiply pi by the radius squared and by the height, with everything in feet. A 12 inch tube has a 0.5 ft radius, so it holds pi x 0.25 = 0.785 cubic feet per foot of height, or 3.14 cubic feet for a 4 foot tube.

About 1.31 eighty-pound bags per foot of height, before waste. A 4 foot tube is 3.14 cubic feet, which is 5.24 bags, so plan on 6. Sonoco’s own chart rounds this to 1 1/3 bags per foot.

An 8 inch tube holds 0.349 cubic feet per foot, about 0.58 eighty-pound bags or 0.78 sixty-pound bags per foot before waste. Sonoco’s chart lists 3/5 and 4/5 bags per foot.

Sonoco lists Builder’s Tube in 6, 8, 10 and 12 inch diameters, round forms from 6 to 36 inches and commercial forms from 6 to 60 inches inside diameter. Availability varies by store, so check locally.

Sonoco lists round forms in 12 foot standard lengths and commercial forms in 12 and 20 foot lengths, with custom lengths available. Its Builder’s Tube brochure lists 4, 8 and 12 foot lengths.

Not always. Sonoco says its Builder’s Tube diameter sizes are nominal and that you should measure if the size is critical. Enter the measured inside diameter with the Custom option for a closer estimate.

The calculator starts at 10 percent, which covers some spillage and concrete left in the mixer. Add more if the hole below the tube is rough or wider than the tube, or estimate that extra concrete separately.

It depends on how many bags you are willing to mix. This tool marks totals up to 1 cu yd as bag-sized and larger totals as worth comparing with a ready-mix delivery; the bagged vs ready-mix calculator compares the two.

No. It only counts the concrete inside the tubes. If your plans call for a footing or a flared base below each tube, estimate it separately and add it to the total.

No. The calculation runs entirely in your browser and nothing you enter is stored or sent anywhere.

• Sonotube Builder’s Tube concrete forms brochure (Sonoco; diameters, lengths and per-foot concrete chart).
• Sonotube round concrete forms brochure (Sonoco brochure hosted by EMI Supply; sizes and cubic yard table).
• Sonotube concrete forming products brochure (Sonoco; round, commercial and FinishFree product lines).
• Sonotube round concrete column forms guide specification (Sonoco; 6 to 60 inch inside diameters).
• QUIKRETE Concrete Mix 1101 data sheet (QUIKRETE; bag yields 0.60, 0.45 and 0.30 cu ft).