How Many Bags of Concrete for a Sonotube?

The short answer

For a 4-foot deep, 10-inch diameter sonotube, buy 3 to 4 80-pound concrete bags. Each bag yields 0.6 cubic feet. The count varies with diameter and depth. Always round up and add one extra for waste.

Key takeaways

Plan ahead: One 80-lb bag yields roughly 0.6 cubic feet of mixed concrete.
Safe estimate: For a 10-inch tube 4 feet deep, buy 4 bags.
Add waste: Always get at least 10% extra for spillage and uneven mixing.
Use a calculator: Our tube calculator gives a precise count for your project.

The humble sonotube is the backbone of many deck and fence projects. Guessing the number of concrete bags can lead to wasted money or a collapsed tube. This guide breaks down exactly how to estimate, calculate, and pour the right amount, saving you time and money.

How many bags of concrete do I need for a sonotube?

For a standard 4-foot deep, 10-inch diameter sonotube, you will need 3 to 4 eighty-pound bags of concrete. The exact number depends on the tube's diameter and depth. An 80-pound bag yields about 0.6 cubic feet of mixed concrete. Use our concrete tube calculator for a precise count. Here is a quick reference for common sizes:

For an 8-inch tube 4 feet deep: about 2 eighty-pound bags.
For a 10-inch tube 4 feet deep: around 3 to 4 bags.
For a 12-inch tube 4 feet deep: around 5 to 6 bags.
Always measure the inner diameter and depth accurately.
Remember to round up and add an extra bag for waste.

How do I calculate the number of concrete bags for a sonotube?

You can calculate the number of bags by finding the volume of the tube and dividing by the yield per bag. Here's the step-by-step process. You can also skip the math and use our bagged concrete calculator to get instant results.

Measure the inner diameter of the sonotube (e.g., 10 inches) and the depth in feet.
Convert the diameter to feet: divide by 12.
Calculate the area: square the radius (half diameter) and multiply by 3.14.
Multiply the area by the depth to get cubic feet.
Divide the cubic feet by the bag yield (0.6 cu ft for 80-lb bags).
Always round up to the next whole bag and add 10% for waste.

How much does it cost to fill a sonotube with concrete?

The cost to fill a sonotube depends on bag price and quantity. As of 2025, an 80-pound bag of concrete mix costs $5 to $7. For a 10-inch tube 4 feet deep, you'll spend about $20 to $28. Larger tubes will, of course, cost more. Use our concrete slab calculator if you're pouring a full slab alongside footings.

8-inch tube: 2 bags × $5–$7 = $10–$14.
10-inch tube: 4 bags × $5–$7 = $20–$28.
12-inch tube: 6 bags × $5–$7 = $30–$42.
Prices may vary by region and bulk discounts. Add extra for rebar, gravel, and mixing tools.
Budget an additional $10 to $20 for a bag of gravel for the base.

What mistakes should I avoid when filling a sonotube?

Many DIYers make avoidable mistakes that lead to weak footings. Always double-check your measurements and account for waste. A common error is underestimating the tube depth due to uneven ground. Check out our gravel calculator to plan the base properly.

Not adding waste: Always buy at least 10% more than the calculated amount to cover spillage and uneven forms.
Measuring the wrong diameter: Use the inner diameter of the tube, not the outer.
Mixing inconsistently: Mix each bag with the exact amount of water stated on the package.
Skipping rebar: Even a single vertical piece of rebar significantly increases strength and crack resistance.
Pouring all at once without tamping: Poke the concrete with a stick or tap the tube to remove air pockets.

What is the best concrete mix for sonotube footings?

For most sonotube projects, a standard 4000 PSI concrete mix is perfect. You can choose between 60-pound and 80-pound bags. The heavier bags offer better value per pound but are harder to handle. For large volumes, consider a ready-mix truck. Our bagged concrete calculator helps you compare options.

60-pound bags: Easier to carry, yield about 0.45 cubic feet. Great for small repairs or if you're working alone.
80-pound bags: The industry standard, yielding about 0.6 cubic feet. More cost-effective per cubic foot.
Ready-mix concrete: Delivered by truck, best for multiple or large-diameter tubes. You'll need a plan for quick placement.
High-strength mix: Use 5000 PSI or higher for heavy structural loads or extreme climates.

Should I pour a sonotube footing myself or hire a pro?

Pouring a sonotube for a deck post or small fence is a manageable DIY job. But if you're building a structural foundation or working with large-diameter tubes, it's smart to call a professional. Proper footing depth and reinforcement are critical for safety. Check your plans with a concrete slab calculator to understand the total scope.

DIY-friendly projects: A single deck post, a mailbox post, or a small pergola. If you can handle the digging and mixing, you can save money.
Hire a pro for: Load-bearing walls, large-diameter sonotubes (over 12 inches), or if the soil is unstable.
When in doubt, ask: Most building departments offer free advice. They can tell you if your plan meets local codes and frost-depth requirements.

Bags needed per cu ft	~2.2 (60-lb)	~1.7 (80-lb)
Yield per bag	~0.45 cu ft	~0.6 cu ft
Weight to carry	Lighter (60 lb)	Heavier (80 lb)

Questions this page answers

How many 60-pound bags of concrete do I need for a 12-inch sonotube?

A 12-inch sonotube 4 feet deep needs about 7 to 8 60-pound bags (since each yields 0.45 cu ft). Always measure carefully and round up.

What size sonotube do I need for a 4x4 post?

For a 4x4 post, use an 8-inch diameter sonotube. This allows enough concrete around the post and proper load distribution. Check local building codes for exact requirements.

How deep should a sonotube footing be?

The footing depth depends on frost line and load. In most regions, 4 feet is common for deck posts, but check with your local building department for frost depth requirements.

Can I mix concrete in the sonotube?

No, you should mix concrete in a wheelbarrow or mixing tray and then pour it into the tube. Mixing in the tube can lead to weak spots and incomplete hydration.

How much water do I need per 80-lb bag?

Each 80-lb bag typically requires about 3 quarts of water, but follow the manufacturer's instructions on the bag for the correct ratio. Too much water weakens the concrete.

Should I use rebar in a sonotube?

Yes, rebar reinforces the concrete and prevents cracking. For most deck footings, one piece of vertical rebar and a few horizontal ties are standard. Confirm with your building plans.

How long does concrete in a sonotube take to cure?

Concrete sets within 24 to 48 hours but reaches full strength in about 28 days. Keep the concrete moist during curing for best results.

Do I need gravel under a sonotube footing?

Yes, a gravel base improves drainage and stability. Place 4 to 6 inches of compacted gravel at the bottom of the hole before setting the tube.

To recap: a typical 4-foot deep, 10-inch sonotube needs 3 to 4 80-pound bags. Always round up and add 10% for waste. For exact numbers tailored to your project, use our concrete tube calculator.