How it works
One cubic yard equals 27 cubic feet. A typical 80-lb bag yields about 0.6 cubic feet, so roughly 45 bags make one yard.
Cubic yards = Length × Width × (Thickness ÷ 12) ÷ 27
How much concrete common projects need
A 10×10 slab poured 4 inches thick needs about 1.2 cubic yards. A 20×20 driveway slab at 6 inches thick needs roughly 7.4 cubic yards.
- Patios and sidewalks: usually 4 inches thick
- Driveways: usually 4 to 6 inches thick
- Footings and steps: check local code for required depth
Bagged mix vs. ready-mix
For small jobs under about one cubic yard, bagged concrete is convenient and you can mix it yourself. For a full slab or large pour, ready-mix delivered by truck is usually cheaper and far less work.
- Bagged: best for small pads, steps, and repairs
- Ready-mix truck: best for slabs and large pours
Tips for ordering concrete
- Add 5 to 10 percent extra for spillage and uneven ground.
- Round up — running short in the middle of a pour is expensive and messy.
- Check the minimum delivery charge if you use ready-mix.