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.
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 table for its QUIK-TUBE forms (data sheet), which come in 8, 10 and 12 in diameters, plus a 6 in column in the table. We ran every cell through this calculator using QUIKRETE Concrete Mix yields, rounded up per tube. 32 of 32 cells match. Each cell shows their count / ours.
| Bag | Depth | 6 in | 8 in | 10 in | 12 in |
|---|---|---|---|---|---|
| 60 lb | 1 ft | 1 / 1 | 1 / 1 | 2 / 2 | 2 / 2 |
| 60 lb | 2 ft | 1 / 1 | 2 / 2 | 3 / 3 | 4 / 4 |
| 60 lb | 3 ft | 2 / 2 | 3 / 3 | 4 / 4 | 6 / 6 |
| 60 lb | 4 ft | 2 / 2 | 4 / 4 | 5 / 5 | 7 / 7 |
| 80 lb | 1 ft | 1 / 1 | 1 / 1 | 1 / 1 | 2 / 2 |
| 80 lb | 2 ft | 1 / 1 | 2 / 2 | 2 / 2 | 3 / 3 |
| 80 lb | 3 ft | 1 / 1 | 2 / 2 | 3 / 3 | 4 / 4 |
| 80 lb | 4 ft | 2 / 2 | 3 / 3 | 4 / 4 | 6 / 6 |
The 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.
“A 40 lb (18.1 kg) bag yields approximately 0.30 ft3 (8.5 L), a 50 lb (22.7 kg) bag yields approximately 0.375 ft3 (10.6 L), a 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L), an 80 lb (36.3 kg) bag yields approximately 0.60 ft3 (17 L) and a 90 lb (40.8 kg) bag yields approximately 0.675 ft3 (19.1 L).”
- QUIKRETE, QUIKRETE® 5000 High Early Strength Concrete Mix (No. 1007) — Product Data Sheet. Checked 2026-09-24.
“YIELD • A 50 lb (22.6 kg) bag yields approximately 0.375 ft3 (10.6 L) • A 60 lb (27.2 kg) bag yields approximately 0.45 ft3 (12.7 L) • An 80 lb (36.2 kg) bag yields approximately 0.60 ft3 (17 L)”
- QUIKRETE, QUIKRETE® Fast-Setting Concrete Mix (No. 1004) — Product Data Sheet (revised November 2025). Checked 2026-09-24.
“YIELD • Each 50 lb (22.6 kg) bag yields approximately 0.375 cu ft (10.6 L) • Each 60 lb (27.2 kg) bag yields approximately 0.45 cu ft (12.7 L) … Start by digging the post hole about 3 times the diameter of the post. Hole depth should be 1/3 the overall post height.”
- Sakrete, Sakrete 5000 Plus High Early Strength Concrete Mix — Technical Data Sheet. Checked 2026-09-24.
“PACKAGE SIZE YIELD WATER REQUIRED SLUMP RANGE 50 lb 22.7 kg 0.38 ft3 0.011 m3 2.1 qts 2.0 L 2 – 3 in 50 – 75 mm 60 lb 27.2 kg 0.47 ft3 0.013 m3 2.5 qts 2.4 L 2 – 3 in 50 – 75 mm 80 lb 36.3 kg 0.6 ft3 0.017 m3 3.5 qts 3.3 L 2 – 3 in 50 – 75 mm … A general rule of thumb is that the depth should be 1/3 the length of the post or pole and the diameter should be 3 times that of the pole or post”
- Sakrete, Sakrete Fast Setting Concrete Mix — Technical Data Sheet. Checked 2026-09-24.
“Post Setting - Based on Average 10” Diameter Hole: … Bag Size Yield Water 50 lb (22.6 kg) 0.38 ft3 (.01 m3) 2.5 to 3 qts (2.4 - 2.9 L) 12” (305 mm) deep 18” (457 mm) deep 1.25 bags 2 bags 24” (610 mm) deep 30” (762 mm) deep 2.5 bags 3 bags”
- QUIKRETE, QUIKRETE® Quantity Calculator. Checked 2026-09-24.
“All yields are approximate and do not include allowance for uneven subgrade, waste, etc.”
- Sakrete, Sakrete Calculators. Checked 2026-09-24.
“PRO TIP: Remember to add 10% to your estimates for safety!”
- 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.
“QUIKRETE® QUIK-TUBES® are available in 4’ (1.2 M) lengths with 8" (203 mm), 10" (254 mm) or 12" (305 mm) diameters. … Table 1: QUIK-TUBE® Capacity Diameter of QUIK-TUBE®(in) Number of bags depth 6“ 8” 10” 12” # of 60# bags 1 foot 1 1 2 2 # of 60# bags 2 feet 1 2 3 4 # of 60# bags 3 feet 2 3 4 6 # of 60# bags 4 feet 2 4 5 7 # of 80# bags 1 foot 1 1 1 2 # of 80# bags 2 feet 1 2 2 3 # of 80# bags 3 feet 1 2 3 4 # of 80# bags 4 feet 2 3 4 6”