Concrete Cylinder Calculator — Sonotube / Tube-Form Footings
Enter the tube diameter, hole depth and number of holes to instantly calculate total concrete volume and how many bags you need for fence posts, deck piers or footings.
Unit system
in
ft
0.267 m³ · 9.42 ft³ · 4 holes
0.0667 m³
per hole- 1
Radius
0.3048 m ÷ 2 = 0.1524 - 2
Cross-section area
π × 0.1524² = 0.07297Circle area = π × r² - 3
Volume per hole
0.07297 m² × 0.914 m = 0.06672 - 4
Total for 4 holes
0.06672 × 4 = 0.2669 - 5
Total in cubic yards
0.2669 m³ ÷ 0.7646 = 0.349
How does this calculator work?
V = π × r² × depth for one hole; multiply by the number of holes. Convert ft³ to bags: one 80 lb bag ≈ 0.60 ft³ (or 60 lb ≈ 0.45, 40 lb ≈ 0.30). A 12" × 36" deep hole needs ~2.36 ft³, or 4 × 80 lb bags. Order 5–10% extra for spillage.
Formula
How this is calculated
Each cylindrical concrete pour is a circle multiplied by its depth: V = π × r² × h, where r is the radius (half the diameter) and h is the depth of the hole. The result in cubic metres is converted to cubic feet and cubic yards for practical use in North America (where concrete bags are measured in ft³ and ready-mix in yd³).
Common tube-form (sonotube) diameters are 6", 8", 10", 12", 16" and 20" (or 150–500 mm in metric). A typical deck-pier hole is 12" diameter by 36" deep — that is roughly 2.36 ft³ or 0.087 yd³ per hole. Four such holes need about 9.44 ft³, requiring 16 × 80 lb bags (each yielding about 0.60 ft³, per Quikrete published data).
Bag counts for 80, 60 and 40 lb bags are all shown so you can choose based on what your supplier carries. Ready-mix is more economical beyond about 1 yd³ total. Add 5–10% extra when ordering; uneven hole sides and spillage are common.
Frequently asked questions
A common rule of thumb is at least one-third of the post height (minimum 18–24" in frost-free zones) and below the frost line in cold climates. For a 6 ft above-ground fence post, a 2 ft depth is typical; for deck piers, consult local building code and soil conditions.
The required footing diameter depends on the load (post spacing, deck size, soil bearing capacity) and local code. A 12" tube is common for residential deck piers; 8" is often used for fence posts and light loads. Always verify with local building requirements.
Bags are convenient for small jobs (a few holes). Once you exceed about 1 yd³ (roughly 45 × 80 lb bags), ready-mix delivered by truck is faster, often cheaper per yard, and easier to control quality. Mix small batches in a wheelbarrow or rent a mixer for mid-size jobs.
Also known as
TG we-Calculate Editorial Team. (2026). Concrete Cylinder Calculator — Sonotube / Tube-Form Footings [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/concrete-cylinder-calculator
TG we-Calculate Editorial Team. "Concrete Cylinder Calculator — Sonotube / Tube-Form Footings." TG we-Calculate. 2026. https://we-calculate.com/calculator/concrete-cylinder-calculator.
TG we-Calculate Editorial Team, "Concrete Cylinder Calculator — Sonotube / Tube-Form Footings," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/concrete-cylinder-calculator
@misc{wecalculate_concrete_cylinder_calculator, title = {Concrete Cylinder Calculator — Sonotube / Tube-Form Footings}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/concrete-cylinder-calculator}}, year = {2026}, note = {TG we-Calculate} }
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