Concrete Column Calculator
Deck piers, fence posts, mailbox posts, pergola columns, and structural building columns all require precise concrete volume calculations. Round columns (poured in Sonotube forms) use the formula π × r² × h; square or rectangular columns use width × depth × height. Enter your column dimensions and quantity to get total cubic yards, 60lb and 80lb bag counts, and a cost estimate. For deck footings and fence posts, fast-setting concrete (Quikrete Fast-Setting No-Mix) is a popular choice — pour dry mix into the hole, add water, and it sets in 20–40 minutes without mixing. For structural building columns, use standard concrete mix and allow the full 28-day cure before loading. The calculator applies a 5% waste factor for columns (less than slabs because there's no form spillage).
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How to Use This Calculator
- 1Enter your measurements in the fields above. Use the units shown next to each field (ft, in, etc.).
- 2Click Calculate to get your material estimate instantly.
- 3Review the highlighted result — it shows the key quantity you need to order.
- 4Use Copy Results to save your estimate, or bookmark the URL — your inputs are encoded in the link.
Pro tip: Always add 10% to your material order to account for waste, cuts, and defects.
Frequently Asked Questions
What size Sonotube do I need for a deck footing?
For a typical 12×12 ft deck bay, a 10-inch or 12-inch diameter Sonotube is standard. The tube diameter should match or exceed the beam width above. A 12-inch tube with fast-setting concrete is the most common choice for deck footings.
How much concrete does a 12-inch column use?
A 12-inch diameter round column 3 feet tall requires approximately 0.087 cubic yards or about 6 bags of 60lb concrete mix. For 4 columns you'd need roughly 24 bags.
Can I use fast-setting concrete for deck footings?
Yes. Fast-setting concrete (Quikrete Fast-Setting Mix or similar) is ideal for deck posts and fence posts. Pour the dry mix directly into the hole around the post, add water, and it sets in 20–40 minutes. No mixing required. Do not use fast-setting concrete for large structural pours — it generates more heat and is harder to work with.
How many columns do I need for a pergola?
Most residential pergolas use 4–6 columns set in the ground or on footings. A 12×16 ft pergola typically uses 4 corner columns. For spans over 16 feet, add intermediate posts every 8 feet. Use 4×4 or 6×6 posts set at least 2 feet deep in concrete for a freestanding pergola.