Concrete Column Calculator
Calculate the concrete needed for round columns, square or rectangular columns, piers and sonotube (cardboard tube) forms. Enter the size, height and number of columns to get the volume, premix bags and site-mix materials.
Calculate column concrete
Column volume formulas
Round column or sonotube
V = π × (d ÷ 2)² × h × Nd = inside diameter, h = height, N = number of columns. π ≈ 3.1416. Use the inside diameter of the form, since the tube wall does not hold concrete.
Square or rectangular column
V = w × d × h × Nw = width, d = depth. For a square column w and d are equal.
Order volume and bags
Vorder = V × (1 + waste%) · Bags = ⌈Vorder × 2,135 ÷ bag kg⌉Columns are formed and poured cleanly, so a 5% waste allowance is usually enough. Cement for a site mix uses the 1.54 dry-volume factor and 1,440 kg/m³ cement density.
Worked examples
- Area = π × 0.15² = 0.0707 m²
- Volume = 0.0707 × 3 × 4 = 0.848 m³
- +5% waste = 0.89 m³
- Premix: 0.891 × 2,135 ÷ 25 = 77 × 25 kg bags; or site mix 1:1.5:3 = 8 × 50 kg cement bags
- Area = π × 0.5² = 0.785 ft²
- Volume = 0.785 × 4 = 3.14 ft³ (0.12 yd³)
- 80 lb bags at 0.60 ft³ each = 3.14 ÷ 0.6 = 5.2 → 6 bags
Concrete per foot of tube
Handy for sonotubes and round piers. Multiply by the depth in feet, then divide by the bag yield (0.60 ft³ for 80 lb, 0.45 ft³ for 60 lb).
| Tube diameter | Volume per foot | 80 lb bags per foot | Volume per metre |
|---|---|---|---|
| 6 in (150 mm) | 0.196 ft³ | 0.33 | 0.018 m³ |
| 8 in (200 mm) | 0.349 ft³ | 0.58 | 0.031 m³ |
| 10 in (250 mm) | 0.545 ft³ | 0.91 | 0.049 m³ |
| 12 in (300 mm) | 0.785 ft³ | 1.31 | 0.071 m³ |
| 16 in (400 mm) | 1.396 ft³ | 2.33 | 0.126 m³ |
| 18 in (450 mm) | 1.767 ft³ | 2.95 | 0.159 m³ |
| 24 in (600 mm) | 3.142 ft³ | 5.24 | 0.283 m³ |
How to use the calculator
- Choose the shape and units. Round for tubes and circular columns, rectangular for boxed formwork.
- Enter the size. Diameter for round columns; width and depth for rectangular ones.
- Enter the height. Measure from the bottom of the pour to the top of the column, including any part below ground.
- Set the number of identical columns and a waste allowance, then calculate.
If the column sits on a spread footing, work out the footing separately with the Concrete Footing Calculator and add the two volumes.
Tips for pouring columns
- Use a strong mix. Structural columns are usually M20–M25 (3,000–3,600 psi) or higher, as specified by the engineer.
- Pour in lifts and vibrate. Fill tall forms in layers and consolidate each one to avoid honeycombing.
- Limit free fall. Concrete dropped more than about 1.5 m (5 ft) can separate; use a tremie or chute for tall columns.
- Brace the form. Wet concrete is heavy; sonotubes and boxed forms must be braced plumb before you pour.
Frequently asked questions
How do I calculate concrete for a round column?
Use π × radius² × height. A column 0.3 m in diameter and 3 m tall holds 3.1416 × 0.15² × 3 = 0.212 m³.
How many bags of concrete for a 12 inch sonotube?
A 12 in tube holds 0.785 ft³ per foot of depth. At 4 ft that is 3.14 ft³, or 6 × 80 lb bags (0.6 ft³ each), or 7 × 60 lb bags.
What mix should I use for concrete columns?
For load-bearing columns, a mix of at least M20 (1 : 1.5 : 3), roughly 3,000 psi, is common. Follow the strength your engineer specifies.
Should I include the footing in the column volume?
No. Calculate the footing or pad separately, then add both volumes together for your order.
Related calculators
Results are estimates for planning. Column sizes, reinforcement and concrete grade for structural work must follow your engineer’s design.