Concrete Volume Calculator
Work out the volume of concrete for a rectangular pour or a round pier — in cubic feet, cubic metres and cubic yards — and how many bags that volume takes.
Concrete volume is the number every other concrete question starts from — but suppliers quote it in cubic yards, drawings use cubic metres, and bags are sold by the cubic foot. This calculator speaks all three, for rectangles and round piers.
Use it to convert a volume, to check a supplier's figure, or to find the bag count for a small pour.
Your results
Enter your measurements and press Calculate.
Quantities are rounded up to whole tiles, planks, boxes or bags, after the wastage allowance. Cost appears only when you enter a price.
Formula
All lengths are converted to a single unit before the calculation: 1 ft = 0.3048 m, 1 in = 25.4 mm, 1 ft² = 0.09290304 m², 1 yd² = 9 ft². Material quantities are rounded up — you cannot buy part of a tile, plank or bag.
How to use this calculator
- Choose rectangular or cylindrical shape.
- For a rectangle, enter length, width and depth. For a round pier, enter diameter and height — the rectangle fields are ignored.
- Set wastage at 10%.
- Enter a bag size to get a bag count.
Worked example
| Round pier | 12 in diameter × 3 ft deep |
|---|---|
| Radius | 12 ÷ 2 = 6 in = 0.5 ft |
| Volume | π × 0.5² × 3 = 2.36 ft³ |
| With 10% wastage | 2.36 × 1.10 = 2.59 ft³ |
| 60 lb bags (0.45 ft³ each) | ⌈2.59 ÷ 0.45⌉ = 6 bags |
Check it by hand: every step above uses the formula in the box. If your numbers match the example inputs but the calculator gives a different answer, please report it via the contact page.
Frequently asked questions
How do I convert cubic feet to cubic yards?
Divide cubic feet by 27 — one cubic yard is 3 ft × 3 ft × 3 ft. So 100 ft³ ÷ 27 = 3.70 yd³. This calculator shows all three units at once.
How do I convert cubic metres to cubic yards?
Multiply cubic metres by 1.308. One cubic metre is 1.31 cubic yards, and 35.31 cubic feet.
What is a sonotube?
A sonotube is a round cardboard form used to cast concrete piers — for decks, fences and posts. You pour concrete into the tube, and the tube is stripped away (or left to rot) after curing. Measure the tube's diameter and the depth of the hole.
Why does the cylindrical result look small?
Round piers are small: a 12 in diameter pier 3 ft deep holds only 2.36 ft³ — about 6 bags of 60 lb mix. Check you entered the diameter in inches, not feet.
Related calculators
Estimates only. Results are for planning. Measure twice, confirm box coverage and tile sizes on the packaging you buy, and follow the manufacturer's instructions. See the disclaimer.