How to Use This Calculator
- Select your project type — slab, footing, or post holes.
- Enter the dimensions. Use the unit toggle for imperial or metric.
- Read your results instantly — cubic yards for truck delivery, or the number of bags if you mix by hand.
Concrete Volume by Project
| Project | Typical Thickness | Example Size | Volume |
|---|---|---|---|
| Sidewalk | 4 inches | 4 ft x 20 ft | 0.99 cu yd |
| Patio | 4 inches | 10 ft x 12 ft | 1.48 cu yd |
| Driveway | 6 inches | 10 ft x 20 ft | 3.70 cu yd |
| Garage floor | 6 inches | 20 ft x 24 ft | 8.89 cu yd |
| Post hole (10" x 36") | n/a | 1 hole | 0.07 cu yd |
Bags vs Ready-Mix: Which to Choose?
For small projects under 0.5 cubic yards (about 14 bags of 80 lb mix), pre-mixed bags are practical. For anything over 1 cubic yard, ready-mix truck delivery is faster, cheaper, and produces a more consistent pour. Most ready-mix companies have a minimum order of 1 cubic yard.
Pre-Mixed Bag Coverage
| Bag Size | Coverage per Bag | Bags per Cubic Yard | Typical Cost |
|---|---|---|---|
| 40 lb | 0.30 cu ft | 90 bags | $3 - $4 |
| 60 lb | 0.45 cu ft | 60 bags | $4 - $6 |
| 80 lb | 0.60 cu ft | 45 bags | $5 - $7 |
Tips for a Successful Pour
- Order 10% extra — concrete always settles into uneven ground and forms. Running short mid-pour is a disaster.
- Prep your subgrade — compact the soil and add 4 inches of compacted gravel for drainage under slabs.
- Use rebar or wire mesh — reinforcement prevents cracking, especially for driveways and slabs over 4 inches thick.
- Cure properly — keep concrete moist for at least 7 days. Rapid drying causes surface cracks.
FAQ
How thick should a concrete slab be?
Standard patios and walkways need 4 inches. Driveways and garage floors should be 5-6 inches. For heavy loads or equipment pads, go 6-8 inches with rebar reinforcement.
How deep should fence post holes be?
The standard rule is one-third of the total post length underground. For a 6-foot fence post, dig 24-36 inches deep. In frost-prone areas, go below the frost line to prevent heaving.
Can I pour concrete in cold weather?
Avoid pouring when temperatures are below 40 degrees F (4 degrees C). Cold weather slows curing and can cause the surface to freeze before it sets. If you must pour in cold weather, use hot water in the mix and cover with insulating blankets.
⚠ Disclaimer
This calculator provides material estimates for planning purposes. Structural concrete work (foundations, load-bearing walls, footings) should be designed by a licensed engineer. Concrete strength, mix design, and reinforcement requirements depend on local building codes and soil conditions. Always obtain required permits before starting structural work.
Prices shown are approximate 2026 U.S. averages and may vary significantly by region, retailer, and market conditions. Always get local quotes for accurate pricing.