Forms and structures · Quantities for columns and piers
Concrete column calculator
Use this concrete column calculator to find the concrete for round or square columns, piers and posts. Choose the shape, enter its size and height and how many you are pouring, add an extra allowance of your own, and see cubic yards, cubic metres and bags.
Concrete column estimate
Measurement system: Imperial. Planning estimate based on the measurements shown below.
Build your estimate
Enter your measurements, then review every step.
The height the concrete fills, not the height of the form or tube if it is only partly filled.
Your choice. The 10% is only the starting entry; uneven bases, forms and spillage decide what you need.
Yields are QUIKRETE's approximate figures. Use the yield printed on your own bag for any other product.
Enter the size of the concrete itself. Diagram not to scale.
Calculation and assumptions
Volume of a round or square column
Worked examples
One round column, 12 in diameter and 8 ft high
Concrete for the column with 10% extra: 0.26 yd³
- Cross-section: π × (0.5 ft)² = 0.7854 ft² (diameter 12 in)
- Volume of one column: 0.7854 ft² × 8 ft = 6.2832 ft³
- In cubic yards: 6.2832 ft³ ÷ 27 = 0.2327 yd³
- With 10% extra: 0.2327 × (1 + 0.1) = 0.256 yd³ (0.1957 m³)
- 80 lb bags: 6.9115 ft³ ÷ 0.6 ft³ per bag = 11.52, rounded up to 12 bags
Four square columns, 16 in × 16 in and 10 ft high
Concrete for 4 columns with 10% extra: 2.9 yd³
- Cross-section: 1.3333 × 1.3333 ft = 1.7778 ft² (16 × 16 in)
- Volume of one column: 1.7778 ft² × 10 ft = 17.7778 ft³
- × 4 columns = 71.1111 ft³
- In cubic yards: 71.1111 ft³ ÷ 27 = 2.6337 yd³
- With 10% extra: 2.6337 × (1 + 0.1) = 2.8971 yd³ (2.215 m³)
- 80 lb bags: 78.2222 ft³ ÷ 0.6 ft³ per bag = 130.37, rounded up to 131 bags
Two round columns, 40 cm diameter and 3 m high, metric
Concrete for 2 columns with 10% extra: 0.83 m³
- Cross-section: π × (0.2 m)² = 0.1257 m² (diameter 40 cm)
- Volume of one column: 0.1257 m² × 3 m = 0.377 m³
- × 2 columns = 0.754 m³
- In cubic yards: 0.754 m³ ÷ 0.7646 = 0.9862 yd³
- With 10% extra: 0.9862 × (1 + 0.1) = 1.0848 yd³ (0.8294 m³)
- 80 lb bags: 29.2893 ft³ ÷ 0.6 ft³ per bag = 48.82, rounded up to 49 bags
| Size (in) | Round ft³ | Round yd³ | Square ft³ | Square yd³ |
|---|---|---|---|---|
| 8 | 2.79 | 0.103 | 3.56 | 0.132 |
| 10 | 4.36 | 0.162 | 5.56 | 0.206 |
| 12 | 6.28 | 0.233 | 8 | 0.296 |
| 16 | 11.17 | 0.414 | 14.22 | 0.527 |
| 20 | 17.45 | 0.646 | 22.22 | 0.823 |
| 24 | 25.13 | 0.931 | 32 | 1.185 |
What the estimate assumes
- The column is a straight prism of one cross-section from bottom to top. Flared tops, belled bases and tapered shapes are not modelled.
- Reinforcement does not reduce the concrete volume here, and its quantity is not calculated.
- A pier poured in a hole is counted by the size you enter. If the hole is larger than the form, use the post-hole calculator or enter the actual diameter.
- This is a quantity estimate, not a design. It does not choose a column size, height, reinforcement or mix. Those come from your plans and a qualified professional.
All example quantities are geometry and arithmetic illustrations. Confirm measurements, product details and ordering rules with your plans and supplier.
Common questions
Concrete column questions
How do I calculate the concrete for a round column?
Find the area of the circle, π × (diameter ÷ 2)², with the diameter in feet, then multiply by the height in feet. That gives cubic feet, and you divide by 27 for cubic yards. For a 12 in column, the radius is 0.5 ft, so the area is about 0.785 ft², and each foot of height takes about 0.785 ft³.
How do I calculate the concrete for a square or rectangular column?
Multiply the two sides, both in feet, to get the area, then multiply by the height. Divide cubic feet by 27 to get cubic yards. Choose Square or rectangular above to enter two different sides.
Is this the same as the Sonotube calculator?
They use the same volume formula for a round column. This page also handles square and rectangular columns and gives the volume per foot of height. The Sonotube page has a chart of common tube sizes. Use whichever matches how you are forming the column.
Can I use it for piers and posts?
Yes, for a pier or post that is a straight round or square column of concrete. A belled or stepped pier is a different shape, and a post set in a hole around a wooden post is better handled with the post-hole calculator.
How many bags of concrete do I need for a column?
Divide the total volume, including your extra, by the bag yield and round up. Choose a bag size above to see the count, using QUIKRETE's approximate yields. Check the yield printed on your own bag.
Does it subtract the rebar?
No. The volume of reinforcement is small and is left in, which slightly overstates the concrete. The calculator also does not choose any reinforcement.
How much extra should I add?
That is your decision from the site conditions. A form that is not perfectly round, an uneven base and spillage all use concrete the geometry does not show. The calculator starts at 10% as an example and shows the allowance separately from the net volume.
Sources
- QUIKRETE Concrete Mix No. 1101 datasheet: Read directly on October 19, 2026. States approximate yields of 0.30, 0.375, 0.45, 0.60 and 0.675 ft³ for the 40, 50, 60, 80 and 90 lb bags.
- NIST: SI Units – Length: Basis for the exact inch-to-centimetre conversion (1 in = 25.4 mm) used in the metric results.