How the number is worked out
volume per tube = π × (diameter ÷ 2)² × height
(diameter and height converted from inches to feet first)
cubic yards = cubic feet ÷ 27
Volume grows with the square of the diameter. Going from an 8 in tube to a 12 in tube is 1.5 times the width but 2.25 times the concrete — the step that most often catches people out when they upsize piers.
Worked example
Six deck piers, filled 48 in high, 80 lb bags:
| Tube | Per tube | Bags shared (6 tubes) | Whole bags per tube |
|---|---|---|---|
| 8 in | 1.40 ft³ | 14 | 3 × 6 = 18 |
| 12 in | 3.14 ft³ | 32 | 6 × 6 = 36 |
If you set post anchors or rebar into the wet concrete, they displace a little; the calculator ignores that, so the count errs slightly high.
How much concrete for a 12 inch Sonotube?
By our arithmetic (π × 0.5² × 1 ft), a 12 in tube holds 0.785 ft³ for every foot of fill height. Multiply by the feet you fill, then by the number of tubes. The bag counts below are this calculator's own, using QUIKRETE Concrete Mix yields of 0.45 ft³ per 60 lb bag and 0.60 ft³ per 80 lb bag (data sheet), rounded up to whole bags per tube.
| Fill height | Volume per tube | 60 lb bags per tube | 80 lb bags per tube |
|---|---|---|---|
| 1 ft | 0.79 ft³ | 2 | 2 |
| 2 ft | 1.57 ft³ | 4 | 3 |
| 3 ft | 2.36 ft³ | 6 | 4 |
| 4 ft | 3.14 ft³ | 7 | 6 |
For six 12 in tubes filled 4 ft high, that is 6 × 6 = 36 bags of 80 lb if each tube gets whole bags. Enter 12 in and your fill height above to get the figure for your own job, including cubic yards. These bag counts are the same as the 12 in column of QUIKRETE's own table, which we check in full below.
Measure the height you will actually fill
Count the part of the tube below grade and the part that sticks up above it. If there is a spread footing at the bottom of the hole, work that out separately with the footing calculator and add the two.
Checked against QUIKRETE's tube table
QUIKRETE prints a bag-count table for its QUIK-TUBE forms (data sheet), for 60 lb and 80 lb bags. We ran every cell of it through this calculator using QUIKRETE Concrete Mix yields, rounded up to whole bags per tube: 32 of 32 cells come out the same. We don't reprint the table here; the link above goes to QUIKRETE's own sheet.
That table doesn't name the concrete product it assumes. Because it matches whole-bag rounding, use the “whole bags per tube” line when you compare.
What this calculator is not for
It does not size piers. Pier diameter, depth and spacing come from your deck plans, the load, your soil and your local frost depth and code — not from a concrete estimate.
Sources
- QUIKRETE, QUIKRETE® Concrete Mix (No. 1101) — Product Data Sheet. Checked 2026-09-24.
- QUIKRETE, QUIKRETE® 5000 High Early Strength Concrete Mix (No. 1007) — Product Data Sheet. Checked 2026-09-24.
- QUIKRETE, QUIKRETE® Fast-Setting Concrete Mix (No. 1004) — Product Data Sheet (revised November 2025). Checked 2026-09-24.
- Sakrete, Sakrete 5000 Plus High Early Strength Concrete Mix — Technical Data Sheet. Checked 2026-09-24.
- Sakrete, Sakrete Fast Setting Concrete Mix — Technical Data Sheet. Checked 2026-09-24.
- QUIKRETE, QUIKRETE® Quantity Calculator. Checked 2026-09-24.
- Sakrete, Sakrete Calculators. Checked 2026-09-24.
- NIST, NIST Handbook 44 (2026), Appendix C — General Tables of Units of Measurement. Checked 2026-09-24.
“1 728 cubic inches (in3) = 1 cubic foot (ft3) 27 cubic feet = 1 cubic yard (yd3)”
- QUIKRETE, QUIKRETE® QUIK-TUBE® Building Forms (No. 6922) — Product Data Sheet. Checked 2026-09-24.