Concrete Calculator
Use this concrete calculator to estimate volume for rectangular slabs, patios, shed pads, and walkways.
Concrete calculator
Adjust the values to estimate material quantity before buying.
Estimated result
Round up for ordering and keep a small project buffer.
- Project area
- 100 sq ft
- Adjusted volume
- 35 cu ft
- Concrete needed
- 1.3 cu yd
- Bags to buy
- 59 bags
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How this estimate works
This calculator turns your project dimensions into a planning quantity, then applies a waste factor so the final number is closer to what you can actually order.
- Cubic feet = length x width x depth in feet
- Cubic yards = cubic feet / 27
- Adjusted volume = volume x (1 + waste percentage)
- Bags needed = adjusted cubic feet / bag yield
Example
A 10 ft by 10 ft slab poured 4 in thick needs about 1.24 cubic yards before rounding.
Common planning notes
- Excavation depth, compacted base, forms, and reinforcement can change project needs.
- Large pours should usually be ordered from a ready-mix supplier instead of bagged concrete.
- Always confirm local code and structural requirements before pouring.
Frequently asked questions
How many cubic feet are in one cubic yard?
One cubic yard equals 27 cubic feet.
How much does an 80 lb bag of concrete yield?
A common estimate is about 0.6 cubic feet per 80 lb bag, but check the product label for the exact yield.
Should I round concrete up?
Yes. Running short during a pour is expensive and stressful, so most estimates include a small waste factor.