Concrete
Concrete Bags Calculator: How Many Bags Do You Need?
Understand concrete bag yields, convert volume into bags, and compare 40, 60 and 80 lb bags (and 20–30 kg bags) with worked examples and a quick reference table.
2 min read
- Dual US / Metric
- +10% Waste Allowance
- Free · Runs in Your Browser
Concrete Column Calculator
Columns and piers are poured into round cardboard tube forms or rectangular wooden forms. Choose the shape, enter the size and height, and the calculator returns the total volume for all columns along with bag quantities.
Enter your measurements
Enter your measurements and press Calculate to see quantities, a material breakdown and an optional cost estimate.
How the calculation works
- Round column: Volume = π × (Diameter ÷ 2)² × Height
- Rectangular column: Volume = Width × Depth × Height
- Total = Volume × Number of columns × (1 + Waste %)
π (pi) is approximately 3.1416. Using the radius (half the diameter) squared is the step people most often get wrong, so double-check that part if calculating by hand.
Assumptions used
- Columns have a constant cross-section from bottom to top.
- Bell-shaped or flared footing bases are not included.
Example calculation
Four 12 in diameter tube-form piers, each 4 ft tall, with 10% waste.
- 1Radius: 12 in ÷ 2 = 6 in = 0.5 ft
- 2Volume per pier: 3.1416 × 0.5² × 4 = 3.14 ft³
- 3Four piers: 3.14 × 4 = 12.57 ft³
- 4With 10% waste: 13.8 ft³ (0.51 yd³)
- 580 lb bags: 13.8 ÷ 0.60 = 23.04 → 24 bags
Result: About 24 × 80 lb bags, or half a cubic yard of ready-mix.
How to measure your project
- Use the inside diameter of the tube form. Common sizes are 8, 10, 12 and 16 in.
- Measure height from the bottom of the form (or hole) to the planned top of concrete, including any part below ground.
- If a pier sits on a wider footing, calculate the footing separately.
Frequently asked questions
How many bags of concrete fill a 12 inch tube form?
A 12 in tube holds about 0.785 ft³ per foot of height. With 80 lb bags yielding 0.60 ft³, that is about 1.3 bags per foot of height before waste.
Do I need rebar in a concrete column?
Structural columns almost always require reinforcement specified by a designer. Rebar does not meaningfully change the concrete volume, but it is essential for strength.
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Results are estimates based on the measurements and assumptions you enter. Always confirm product specifications, local building codes and final quantities with your supplier or a qualified professional. See our disclaimer.