Concrete Calculator
Enter your project dimensions to instantly calculate cubic yards, cubic feet, and bags needed — for slabs, columns, and walls.
Project type
4″ is standard for driveways
8″ is common for foundation walls
Results
Cubic Yards
—
yd³
Cubic Feet
—
ft³
40 lb Bags
—
bags needed
60 lb Bags
—
bags needed
80 lb Bags
—
bags needed
How to Calculate Concrete
Concrete volume is calculated by multiplying the length, width, and thickness of your project. The result in cubic feet is then divided by 27 to convert to cubic yards — the standard unit used when ordering ready-mix.
For slabs: Volume (ft³) = Length × Width × (Thickness ÷ 12). For round columns: Volume = π × radius² × height × count.
Bag Concrete Coverage
| Bag Size | Yield (cu ft) | Yield (cu yd) |
|---|---|---|
| 40 lb bag | 0.30 ft³ | 0.011 yd³ |
| 60 lb bag | 0.45 ft³ | 0.017 yd³ |
| 80 lb bag | 0.60 ft³ | 0.022 yd³ |
For projects over 1 cubic yard, ordering ready-mix concrete is usually more cost-effective than buying bags.
Frequently Asked Questions
- How thick should a concrete slab be?
- Most residential slabs — patios, garage floors, driveways — are 4 inches thick. High-traffic areas may need 5–6 inches. Sidewalks are typically 3–4 inches.
- Should I add a waste factor?
- Yes. Adding 10% is standard practice. It accounts for spillage, uneven subgrade, and form overages. Having a little extra is far better than running short mid-pour.
- How many cubic yards does a concrete truck hold?
- A standard ready-mix truck holds 8–10 cubic yards. Most suppliers have a minimum order, often around 1 yard, and may charge extra for short loads.