How to calculate concrete
80 lb bags = Cubic feet ÷ 0.60
Example: a 10 ft × 10 ft patio at 4 inches is 100 × 4 ÷ 12 = 33.3 cubic feet = 1.23 cubic yards. That is about 56 bags of 80 lb — or one small ready-mix load.
How thick should a slab be?
| Project | Typical thickness |
|---|---|
| Sidewalks, patios, shed floors | 4 in |
| Driveways (cars) | 4–5 in |
| Driveways (heavier vehicles), garage slabs | 5–6 in |
Bags or ready-mix?
An 80 lb bag yields about 0.6 cubic feet, so one cubic yard takes about 45 bags of 80 lb (60 bags of 60 lb, 90 bags of 40 lb). Mixing that by hand is hard work. Beyond 1–2 yards, ready-mix delivered by truck is usually cheaper and gives a more consistent pour. Enter both prices to compare.
Frequently asked questions
How many 80 lb bags of concrete make a yard?
About 45 bags (27 cu ft ÷ 0.60 cu ft per bag).
How many 60 lb bags make a yard?
About 60 bags (27 ÷ 0.45).
How much does a yard of concrete weigh?
About 4,000 lb — roughly 2 US tons.
How much extra concrete should I order?
5–10% is typical to cover uneven ground and spillage. Running short mid-pour is far worse than having a little left.
Related calculators
These figures are estimates for planning only. Material weights and coverage vary by supplier, moisture and compaction. Always confirm quantities and prices with your supplier before ordering. See our terms & disclaimer.