Sixteenth
Concrete Calculator
Pick a slab or a round column, enter the size, and get the cubic yards to order or the number of premix bags to buy, with extra for waste.
Plain numbers use the unit in the label. You can also type 3' 6", 42 in or 1.2 m.
How much concrete you need
slab: length × width × thickness · round: π × (diameter ÷ 2)² × height
cubic yards = cubic feet ÷ 27
Ready-mix trucks sell by the cubic yard, usually with a one-yard minimum. For small pours, premix bags are simpler:
| Bag | Yield | Bags per cubic yard |
|---|---|---|
| 80 lb | about 0.60 ft³ | 45 |
| 60 lb | about 0.45 ft³ | 60 |
| 40 lb | about 0.30 ft³ | 90 |
Typical thicknesses: 4" for patios and walks, 5–6" for driveways, and footings at least as deep as your local frost line requires.
Questions
How do I calculate cubic yards of concrete?
Multiply length × width × thickness in feet to get cubic feet, then divide by 27. A 10' × 12' slab 4" thick is 10 × 12 × 0.333 = 40 ft³, or 1.48 yd³. Add 5–10% for waste, uneven grade and spillage.
How many 80 lb bags of concrete make a yard?
An 80 lb bag of premix makes about 0.6 ft³, so a cubic yard (27 ft³) takes about 45 bags. A 60 lb bag makes about 0.45 ft³ (60 bags per yard) and a 40 lb bag about 0.30 ft³ (90 bags per yard).
How much concrete for a sonotube?
Volume = π × (diameter ÷ 2)² × height. A 12" tube 4' deep holds π × 0.5² × 4 = 3.14 ft³, about six 80 lb bags with waste.