Concrete Calculator
Measure the longest side
Measure the shorter side
Standard is 4" for patios, 6" for driveways
How to Use This Calculator
For Slabs (Patios, Driveways)
- Measure the length and width in feet
- Determine thickness (4" for patios, 6" for driveways)
- Add 5-10% waste factor for overages
- Review results for cubic yards needed
Understanding Results
- Cubic Yards: Order this amount from ready-mix supplier
- Bag Count: For small projects under 1 yard
- Cost Estimate: Based on average regional pricing
- Waste Factor: Accounts for spillage and variations
Common Concrete Projects
Patio Slab
10' × 12' × 4" thick
= 1.48 cubic yards
= 67 bags (80 lb)
Driveway
20' × 20' × 6" thick
= 7.41 cubic yards
= Ready-mix recommended
Fence Posts
10 posts, 8" dia × 2' deep
= 0.26 cubic yards
= 12 bags (80 lb)
Professional Tips
The 81 Rule
For quick estimates on 4-inch slabs, professionals use this formula:
Example: 324 sq ft ÷ 81 = 4 cubic yards
Order Extra
Always order 5-10% more than calculated. Running short costs more than having extra.
Timing Matters
Schedule ready-mix delivery for early morning. You'll have 90 minutes to work with the concrete.
Weather Considerations
Avoid pouring in extreme heat (>90°F) or when freezing temps are expected within 24 hours.
Frequently Asked Questions
How accurate is this calculator?
Our calculator is accurate within 5% for standard shapes. Complex projects may require professional estimation. Always add 5-10% waste factor for safety.
Should I use bags or ready-mix?
For projects under 1 cubic yard, bags are practical. Over 1 yard (about 45 bags), ready-mix is more cost-effective and saves significant labor time.
What's the difference between 60lb and 80lb bags?
80lb bags yield about 0.6 cubic feet, while 60lb bags yield 0.45 cubic feet. 80lb bags are more economical but heavier to handle. Choose based on your physical capability.
How much does concrete cost?
Ready-mix concrete typically costs $120-180 per cubic yard. Bagged concrete costs about $5-7 per 80lb bag. Labor, delivery, and finishing add to total project cost.