Concrete Column & Footing Calculator (Round)
By Santaji GadepatilinUpdated October 27, 2026
Round columns and footings need an exact volume of concrete to order the right number of bags or cubic metres. The volume comes from the diameter and height. This free concrete column & footing calculator solves for whichever value you leave blank and shows the formula and steps.
How to use the concrete column & footing calculator
Enter the column diameter, height (or hole depth) and the number of columns. The total volume and 40 kg bags (with 5% extra) are calculated.
Concrete column & footing formula
V = π × (d ÷ 2)² × h × n
Example
Six piers, 300 mm diameter and 1.2 m deep:
V = π × 0.15² × 1.2 × 6 = 0.509 m³ → about 30 bags
Concrete per metre of column height
| Diameter / size | Volume per metre | 40 kg bags per metre |
|---|---|---|
| Ø 150 mm round | 0.0177 m³ | 2 |
| Ø 200 mm round | 0.0314 m³ | 2 |
| Ø 250 mm round | 0.0491 m³ | 3 |
| Ø 300 mm round | 0.0707 m³ | 5 |
| Ø 400 mm round | 0.1257 m³ | 8 |
| Ø 450 mm round | 0.1590 m³ | 10 |
| Ø 600 mm round | 0.2827 m³ | 17 |
| 230 × 230 mm square | 0.0529 m³ | 4 |
| 300 × 300 mm square | 0.0900 m³ | 6 |
| 400 × 400 mm square | 0.1600 m³ | 10 |
| 450 × 450 mm square | 0.2025 m³ | 12 |
Sonotubes and footings
Round forms (cardboard tubes) are common for deck and porch footings. Add the volume of any spread footing at the base: a 600 × 600 × 300 mm pad is 0.108 m³.
Reinforcement
Structural columns need steel reinforcement designed by an engineer. Check minimum cover (often 40 mm for columns) and use the rebar weight calculator to estimate steel.
Pouring tips
- Pour in layers and vibrate or rod each one to remove air pockets.
- Avoid dropping concrete more than about 1.5 m freely to prevent segregation.
- Keep exposed tops damp for at least 7 days while curing.
Square columns
For square or rectangular columns, use width × depth × height instead.
Frequently asked questions
How much concrete for a post hole?
Volume = π × radius² × depth. A 300 mm hole 1.2 m deep needs about 0.085 m³ — roughly 5 bags of 40 kg pre-mix.
Do I subtract the post?
For accuracy, yes — subtract the post's volume below ground. For wooden posts it is usually small.
Does the bag count include waste?
Yes, 5% extra is added.
How much concrete is in a 300 mm × 3 m column?
π × 0.15² × 3 = 0.212 m³.
How many bags for a 200 mm post hole 1 m deep?
About 0.031 m³, or 2 bags of 40 kg pre-mix (plus waste).