Concrete Calculator
Typical Thicknesses
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Concrete Guide
Understanding Concrete
Concrete is a mixture of cement, water, sand, and gravel that hardens over time. It's one of the most widely used construction materials in the world, valued for its strength, durability, and versatility.
Bags vs Ready-Mix
Pre-Mixed Bags
- • Good for small projects (<1 cubic yard)
- • Available at hardware stores
- • Just add water and mix
- • 40, 60, or 80 lb bags
- • Higher cost per cubic yard
Ready-Mix Delivery
- • Best for large projects (>1 cubic yard)
- • Delivered by truck
- • Pre-mixed to specifications
- • More cost-effective at scale
- • Minimum order often required
Concrete Bag Coverage
| Bag Size | Coverage | Bags per Cubic Yard |
|---|---|---|
| 40 lb | 0.30 cu ft | ~90 bags |
| 60 lb | 0.45 cu ft | ~60 bags |
| 80 lb | 0.60 cu ft | ~45 bags |
Project Guidelines
Sidewalks & Patios
- • Minimum 4" thick
- • 4" gravel base recommended
- • Control joints every 8-12 feet
- • Slope for drainage (1/4" per foot)
Driveways
- • Minimum 4" thick (6" for heavy vehicles)
- • Reinforcement mesh or rebar
- • Proper subgrade compaction
- • Thicker at edges (6")
Footings
- • Depth below frost line
- • Width 2× wall thickness
- • Reinforced with rebar
- • Check local building codes
Posts & Columns
- • Diameter: 3× post size
- • Depth: 1/3 of post length
- • Below frost line
- • Crown top for water runoff
Tips for Success
Important Safety Note
Wet concrete is caustic and can cause chemical burns. Always wear gloves and protective clothing. Wash any skin contact immediately with water. For larger projects, check local building codes and permit requirements.
Frequently Asked Questions
How do I calculate concrete for a slab?
Multiply length x width x thickness (all in feet) to get cubic feet, then divide by 27 to convert to cubic yards. For example, a 10x12 foot slab that's 4 inches thick: 10 x 12 x 0.33 = 39.6 cubic feet = 1.47 cubic yards. Order 10% extra for waste.
How many bags of concrete do I need?
It depends on bag size: 40 lb bags yield 0.30 cubic feet (90 bags per cubic yard), 60 lb bags yield 0.45 cubic feet (60 bags per yard), and 80 lb bags yield 0.60 cubic feet (45 bags per yard). For projects over 1 cubic yard, consider ready-mix delivery.
How thick should my concrete slab be?
Sidewalks and patios need minimum 4 inches, driveways need 4-6 inches (6 inches for heavy vehicles), garage floors need 4-6 inches, and foundations typically need 8-12 inches. Always check local building codes for requirements.
Should I use bagged concrete or ready-mix?
Use bagged concrete for small projects under 1 cubic yard (about 45 bags of 80 lb mix). For larger projects, ready-mix delivery is more cost-effective and ensures consistent quality. Ready-mix trucks typically have minimum orders of 1-3 cubic yards.