How to measure a tube form
- Diameter: use the tube's inside diameter, the size printed on the form (8, 10, 12 in and so on).
- Height: measure the full length that will be filled, from the bottom of the hole to the top of the tube, not just the part above ground.
- Quantity: enter how many tubes of that size you're pouring. Add another part for tubes of a different size or height.
- Footing pads or bells: if the tube sits on a spread footing, add a pad footing or bell footing part so the base is counted too.
How tube volume is calculated
A tube is a cylinder: π × (diameter ÷ 2)² × height. Halve the diameter to get the radius, square it, multiply by π (about 3.1416) and by the height, with everything in feet. Multiply by the number of tubes, then divide by 27 for cubic yards. Here is one 12 in tube, 4 ft tall:
Column
- Diameter: 12 in ÷ 12 = 1 ft
- Height: 4 ft
- Quantity: 1
- Radius: 1 ft ÷ 2 = 0.5 ft
- Cross-section area: π × (0.5 ft)² = 0.7854 ft²
- One column: 0.7854 ft² × 4 ft = 3.1416 ft³
- All columns: 3.1416 ft³ × 1 = 3.1416 ft³
Total and order
- In cubic yards: 3.1416 ft³ ÷ 27 = 0.1164 yd³
- With 5% extra: 0.1164 yd³ × 1.05 = 0.1222 yd³
- Order, rounded up to the next 0.25 yd³: 0.25 yd³
With 5% extra, that one tube takes 6 80-lb bags or 8 60-lb bags. The calculator defaults to 5% for tubes because the form holds the concrete to an exact size; raise it if the bottom of the hole is wider than the tube.
Doubling the diameter quadruples the concrete. A 24 in tube holds four times as much as a 12 in tube of the same height, so check the size on the plan before buying bags.
Sonotube size chart
Concrete per foot of tube, and bags to fill a tube 4 ft tall with 5% extra. Yields from the QUIKRETE data sheet: 0.60 ft³ per 80-lb bag, 0.45 ft³ per 60-lb bag.
| Tube | ft³ per ft | yd³ per ft | 80-lb bags per ft | 80-lb bags, 4 ft tube | 60-lb bags, 4 ft tube |
|---|---|---|---|---|---|
| 6 in | 0.196 | 0.0073 | 0.33 | 2 | 2 |
| 8 in | 0.349 | 0.0129 | 0.58 | 3 | 4 |
| 10 in | 0.545 | 0.0202 | 0.91 | 4 | 6 |
| 12 in | 0.785 | 0.0291 | 1.31 | 6 | 8 |
| 14 in | 1.069 | 0.0396 | 1.78 | 8 | 10 |
| 16 in | 1.396 | 0.0517 | 2.33 | 10 | 14 |
| 18 in | 1.767 | 0.0654 | 2.95 | 13 | 17 |
| 20 in | 2.182 | 0.0808 | 3.64 | 16 | 21 |
| 24 in | 3.142 | 0.1164 | 5.24 | 22 | 30 |
Tips for tube forms
- Calculate every tube together. Eight 12 in tubes, 3½ ft tall, need 0.81 yd³: 39 80-lb bags with 5% extra. Set the quantity instead of adding up tubes by hand.
- Fill in lifts. Place and rod the concrete in layers so it fills the tube without voids, especially in tall forms.
- Brace tall forms. A tube full of wet concrete is heavy. See the weight figure under the result before you start.
- Check footing sizes with your inspector or plans. Tube diameter and depth for decks and porches are usually set by local code and loads.
Questions people ask
How many bags of concrete for a 12-inch sonotube?
A 12 in tube 4 ft tall holds 3.14 ft³ (0.12 cubic yards). With 5% extra that's 6 80-lb bags or 8 60-lb bags.
How much concrete per foot of 8-inch tube?
Each foot of an 8 in tube holds 0.35 ft³ of concrete. With 5% extra, that's 1 80-lb bag per foot, or 1 50-lb bags.
How many 80-lb bags fill a 10-inch tube 4 ft deep?
4 bags, including 5% extra. The tube holds 2.18 ft³, and each 80-lb bag yields 0.60 ft³.
Which diameter do I measure on a tube form?
Use the inside diameter, which is the size printed on the form (8, 10, 12 in and so on). Measure the height from the bottom of the hole to the top of the form, not just the part above ground.
How much concrete for 6 deck footings?
Six 12 in tubes, each 4 ft tall, need 0.7 cubic yards. With 5% extra, order 0.75 yd³ or buy 33 80-lb bags. Set the quantity field to 6 to calculate them together.
Related calculators
Sources
- QUIKRETE Concrete Mix No. 1101 product data sheet, retrieved October 2, 2026
- SAKRETE High-Strength Concrete Mix technical data sheet, retrieved October 2, 2026
- NRMCA, Concrete in Practice 31: Ordering Ready Mixed Concrete, retrieved October 2, 2026
- NRMCA, Concrete in Practice 36: Structural Lightweight Concrete, retrieved October 2, 2026
Last updated October 2, 2026. Read how we calculate, including formulas, waste defaults and rounding.