How to Estimate Concrete: Yards, Bags, and Avoiding Waste
Published Apr 14, 2026 Β· 5 min read
Concrete is sold by the cubic yard (27 cubic feet). Ordering too little means a weak cold joint; too much means paying for waste. Here's how to calculate exactly what you need.
The Basic Formula
Volume = Length Γ Width Γ Depth (all in feet), then divide by 27 to get cubic yards.
10 ft Γ 10 ft slab, 4 inches thick: 10 Γ 10 Γ 0.333 = 33.3 cu ft Γ· 27 = 1.23 cubic yards
Common Project Estimates
| Project | Typical Depth | Example Size | Cubic Yards |
|---|---|---|---|
| Patio slab | 4" | 12Γ16 ft | 2.4 |
| Driveway | 5" | 10Γ40 ft | 6.2 |
| Sidewalk | 4" | 3Γ50 ft | 1.9 |
| Footings | 12" | 8"Γ100 ft | 2.5 |
| Steps (each) | varies | 3Γ4 ftΓ7" | 0.06 |
Bags vs. Truck Delivery
| Bags (80 lb) | Ready-mix truck | |
|---|---|---|
| Coverage | 0.022 cu yd each | Minimum 1 yard |
| Cost | ~$6-7/bag ($270/yd) | $140-200/yd |
| Best for | Under 1 cubic yard | Over 1 cubic yard |
| Mixing | Manual or mixer | Ready to pour |
At about 45 bags per yard, anything over 1 yard is significantly cheaper and easier with truck delivery.
Always Over-Order
- Add 10% extra for waste, spillage, and form irregularities
- Uneven ground can easily add 5-10% to your volume
- It's far better (and cheaper) to have a little extra than to run short
- Short pours require cold joints that compromise structural integrity
Try it: Use our Concrete Calculator to get exact volume, bag count, and cost for your project.