Enter your dimensions to find out how many cubic yards or bags of concrete you need — for slabs, footings, columns, and steps.
All concrete is measured by volume. The formula for a slab is: length × width × thickness. Divide by 27 to get cubic yards (the unit ready-mix trucks use). This calculator handles slabs, footings (rectangular), and round columns, then adds everything up so you can order or buy bags in one go.
For small jobs under about 1 cubic yard, bagged concrete is usually easiest — available at any hardware store. For larger pours, ordering ready-mix by the truck is cheaper and much faster. Most ready-mix trucks carry 8–10 cubic yards. Add 5–10% extra to account for spillage, uneven sub-base, and waste.
| Bag size | Yields | Bags per yd³ |
|---|---|---|
| 40 lb | 0.011 yd³ (0.30 ft³) | ~90 |
| 60 lb | 0.017 yd³ (0.45 ft³) | ~60 |
| 80 lb | 0.022 yd³ (0.60 ft³) | ~45 |
Sidewalks and patios: 4 inches. Driveways: 4–6 inches (6 for heavy vehicles). Garage floors: 4–6 inches. Structural slabs: consult an engineer. Always pour on compacted gravel sub-base for best results.
Dampen the sub-base before pouring so it doesn't pull water from the concrete too fast. Work in sections for large slabs, and never add extra water to the mix — it weakens the finished concrete significantly. Control joints every 8–12 feet prevent cracking.