Pouring a slab or setting posts? Get the exact volume and number of bags.
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Concrete volume = length × width × thickness for slabs, or π × radius² × depth for round holes and columns. Convert to cubic yards by dividing cubic feet by 27.
An 80 lb bag of premix makes about 0.6 cubic feet, so a 10 × 10 ft slab 4 in thick (1.23 yd³) needs about 56 bags plus waste. For more than about a cubic yard, ready-mix delivery is usually easier and cheaper.
| Units | Feet & inches |
| Shape | Slab, patio or footing (rectangle) |
| Length / height (ft or m) | 10 |
| Width (ft or m) | 10 |
| Thickness (in or cm) | 4 |
| Diameter (in or cm, round) | 12 |
| How many | 1 |
| Waste allowance | 10% |
| Bag size | 80 lb |
| Price per bag (optional) | 0 |
| Currency | $ |
| Concrete needed | 1.36 yd³ · 36.7 ft³ · 1.04 m³ |
| Bags of 80 lb premix | 62 bags |
| Without waste allowance | 1.23 yd³ · 33.3 ft³ · 0.94 m³ |
| Ready-mix truck | 1.5 yd³ (order in ¼ yd steps) · 1.1 m³ |
1.36 yd³ · 36.7 ft³ · 1.04 m³; 62 bags.
| Units | Metres & centimetres |
| Shape | Round column or post hole |
| Length / height (ft or m) | 1 |
| Width (ft or m) | 10 |
| Thickness (in or cm) | 4 |
| Diameter (in or cm, round) | 30 |
| How many | 4 |
| Waste allowance | 10% |
| Bag size | 25 kg |
| Price per bag (optional) | 0 |
| Currency | $ |
| Concrete needed | 0.41 yd³ · 11 ft³ · 0.31 m³ |
| Bags of 25 kg premix | 29 bags |
| Without waste allowance | 0.37 yd³ · 10 ft³ · 0.28 m³ |
| Ready-mix truck | 0.5 yd³ (order in ¼ yd steps) · 0.4 m³ |
29 bags.
At 4 inches thick: about 56 × 80 lb bags, or 62 with 10% waste.
81 sq ft at 4 inches thick, or 54 sq ft at 6 inches.
4 inches for patios and paths, 5–6 inches for driveways and garage floors.
Roughly one to two 50 lb bags per post for a 10–12 in hole about 2–3 ft deep.