Key Takeaways
- Concrete is sold by the cubic yard (27 cubic feet) for ready-mix delivery
- Always add 10% extra for waste, spillage, and uneven subgrade
- Projects over 1 cubic yard are usually more economical with ready-mix delivery
- Standard slab thickness: 4 inches for patios, 6 inches for driveways
- Allow 28 days for concrete to reach full strength
Understanding Concrete Calculations
Concrete is sold by the cubic yard (27 cubic feet) for ready-mix delivery or by the bag for smaller DIY projects. Accurately calculating your concrete needs prevents costly overages or project delays from running short.
Recommended Slab Thickness
| Application | Thickness | Strength (PSI) |
|---|---|---|
| Sidewalks/Walkways | 3-4 inches | 3,000 |
| Patios | 4 inches | 3,000 |
| Residential Driveways | 4-6 inches | 3,500-4,000 |
| Garage Floors | 6 inches | 3,500 |
| Commercial/Heavy Use | 6-8 inches | 4,000+ |
Bags vs Ready-Mix
| Bag Size | Coverage | Best For |
|---|---|---|
| 40 lb bag | 0.011 cu yd | Small repairs |
| 60 lb bag | 0.017 cu yd | Posts, small projects |
| 80 lb bag | 0.022 cu yd | DIY slabs <1 cu yd |
| Ready-Mix Truck | 1+ cu yd | Projects >1 cu yd |
Pro Tip: When to Order Ready-Mix
For projects requiring more than 1 cubic yard of concrete, ready-mix is generally more economical and ensures consistent quality. Most concrete trucks deliver a minimum of 1 cubic yard, with full trucks carrying 8-10 cubic yards. Expect to pay a short-load fee for orders under the minimum.
Concrete Tips for Success
- Always add 10% extra for waste, spillage, and uneven subgrade
- Prepare your forms and subgrade before concrete arrives
- Have enough helpers ready - concrete waits for no one
- Wet the subgrade before pouring to prevent moisture absorption
- Use wire mesh or rebar for added strength
- Allow proper curing time (7 days minimum, 28 days for full strength)
- Keep concrete moist during curing with plastic or wet burlap
Weather Considerations
Temperature significantly affects concrete curing. Avoid pouring when temperatures will drop below 40F within 24 hours or rise above 90F. Hot weather accelerates setting time, while cold weather slows curing and can cause cracking. Ideal pouring conditions are 50-70F.