Sonotube Calculator

By Uzair Arshad , Senior Civil and Structural Engineer

Last updated: April 20, 2026

Use this free Sonotube concrete calculator to estimate how much concrete you need for round form footings. Enter your tube diameter, depth, and quantity to get cubic yards, cubic feet, and bag counts for 60 lb and 80 lb mix.

How to use this calculator

This Sonotube calculator helps you estimate concrete volume for round form footings. Enter diameter, depth, quantity, and waste factor, then the Sonotube calculator returns cubic yards, cubic feet, and bag counts.

Measure the inside diameter of your tube in inches. Common sizes are 8, 10, 12, 16, and 18 inches. Use the actual tube size you plan to buy, not a rough guess.
Measure required depth in inches from top of finished grade to the bottom of footing. Many cold-climate US locations require footing bottoms at 36 to 48 inches below grade to stay below frost line.
Count total footing locations. For deck framing, this usually equals your number of support posts unless your plan includes special corner or beam conditions.
Set waste factor. Use 5% for clean forms and controlled pours. Use 10% for most DIY jobs where tubes are hand-cut or soil irregularities can change actual depth.
Click "Calculate concrete volume" to get cubic yards, cubic feet, 80 lb and 60 lb bag counts, and both bag-mix and ready-mix budget ranges.

Common Sonotube sizes and concrete volume per foot of depth

Use this quick table to sanity-check Sonotube calculator results before ordering materials.

Tube diameter	Concrete per 1 ft depth	Concrete per 4 ft tube	Typical use
8 in	0.35 cu ft	1.40 cu ft	Light deck and fence post footings
10 in	0.55 cu ft	2.18 cu ft	Medium deck posts in firm soils
12 in	0.79 cu ft	3.14 cu ft	Common 4x4 and some 6x6 layouts
16 in	1.40 cu ft	5.58 cu ft	Heavier beams and soft soils
18 in	1.77 cu ft	7.07 cu ft	Large tributary load footings

How the calculation works

Geometry:
Radius (ft) = (Tube Diameter (in) / 12) / 2
Depth (ft) = Tube Depth (in) / 12
Volume per Tube (cu ft) = π × Radius² × Depth

Total Volume:
Total Volume (cu ft) = Volume per Tube × Number of Tubes
With Waste (cu ft) = Total Volume × (1 + Waste % / 100)
Cubic Yards = Total with Waste / 27

Bag Count:
80 lb Bags = Total with Waste / 0.60 (rounded up)
60 lb Bags = Total with Waste / 0.45 (rounded up)

Tube Diameter: Inside diameter of the Sonotube form in inches
Tube Depth: Height of the tube from grade to footing bottom in inches
Number of Tubes: Total Sonotube footings in your project
Waste %: Extra percentage for spillage and uneven tube cuts

This Sonotube calculator uses cylinder volume math, then converts the result into practical ordering units. You get cubic feet for bag planning and cubic yards for ready-mix ordering, with a waste factor added so your estimate matches real jobsite conditions.

Example calculation

Four 12 inch Sonotubes, each 48 inches deep, with 10% waste:

Radius = (12 / 12) / 2 = 0.5 ft
Depth = 48 / 12 = 4 ft
Volume per tube = π × 0.5² × 4 = 3.14 cu ft
Total volume = 3.14 × 4 = 12.57 cu ft
With 10% waste = 12.57 × 1.10 = 13.82 cu ft
Cubic yards = 13.82 / 27 = 0.51 cu yd
80 lb bags = 13.82 / 0.60 = 24 bags (rounded up)
60 lb bags = 13.82 / 0.45 = 31 bags (rounded up)

For a full walkthrough with size comparison tables and real-world waste tips, see our guide on how much concrete you need for sonotubes.

Concrete bag yield quick guide

Use this table to compare bag count and labor before you buy. Actual yield varies slightly by water ratio and site temperature.

Mix size	Approx. yield per bag	Typical 2026 price	Best use case
60 lb concrete mix	~0.45 cu ft	$5.00 to $7.50	Small repairs and 1 to 3 footings
80 lb concrete mix	~0.60 cu ft	$6.50 to $9.00	Most DIY footing projects
Ready-mix delivery	Sold by cubic yard	$170 to $220 per yard	Larger pours, tighter schedule, consistency

Assumptions and limitations

This Sonotube calculator assumes the tube is a perfect cylinder with uniform inside diameter and depth. Real forms sometimes flare slightly at the bottom or compress in soft soil, which can change actual volume by 2% to 5%.

Bag yields (0.60 cu ft per 80 lb bag and 0.45 cu ft per 60 lb bag) are based on manufacturer specs at standard water ratios. Mixing too wet reduces yield and weakens the pour.

Common Sonotube calculator mistakes

The first mistake is using the wrong tube diameter from a rough estimate instead of the product label.

The second mistake is missing frost depth. In many US regions, footings must extend below frost line, often 36 to 48 inches, and shallow holes can fail inspection.

The third mistake is ordering no extra mix. Even careful pours lose concrete to spill, over-excavation, and uneven cuts, so a 5% to 10% waste buffer is usually cheaper than a last-minute material run.

Frequently Asked Questions

How do you calculate concrete for a Sonotube?

Use cylinder volume. Convert tube diameter and depth to feet, then calculate pi times radius squared times depth. Multiply by the number of tubes and divide by 27 for cubic yards. Add 5% to 10% waste so your crew does not run short during the pour.

How many bags of concrete does a 12 inch Sonotube need?

A 12 inch Sonotube at 48 inches deep needs about 3.14 cubic feet before waste. That is about 6 bags of 80 lb mix or 7 bags of 60 lb mix. With a 10% waste factor, most jobs plan closer to 6 to 7 eighty-pound bags per tube.

How many bags of concrete does an 8 inch Sonotube need?

An 8 inch Sonotube at 48 inches deep needs about 1.40 cubic feet before waste. That usually rounds to 3 bags of 80 lb mix or 4 bags of 60 lb mix. Add waste and round up because tube tops and subgrade are rarely perfectly uniform.

How do you calculate Sonotube volume?

Measure tube diameter and depth in inches, then convert both to feet. Calculate pi times radius squared times depth to get cubic feet per tube. Multiply by your tube count for total volume and divide by 27 for cubic yards. This is standard cylinder math applied to a round concrete form.

How many bags of concrete does an 18 inch Sonotube need?

An 18 inch Sonotube at 48 inches deep holds about 7.07 cubic feet of concrete before waste. That works out to 12 bags of 80 lb mix or 16 bags of 60 lb mix. At this size most crews switch to ready-mix delivery because hand-mixing 12+ bags per hole is slow and tiring.