How Much Concrete Do I Need?
Calculate the exact amount of concrete for any project. Enter your dimensions below to get cubic yards, bag counts, and cost estimates.
Decision Guide
What to buy after you know the volume
Once the result is over about 1 cubic yard, a truck order is usually easier than hauling bags. Under that line, bags can still be practical if the transport and mixing work are manageable.
Ready-mix is the safer default
Plan around 1.36 yd³ with waste, or about 62 bags if you mix it yourself.
Small truck orders often carry delivery fees, so compare that against bag hauling and mixing time.
Before you order
- Waste-adjusted order size matters more than the raw cubic-yard number.
- Bag count becomes a labor problem before it becomes a math problem.
- National price averages are planning inputs, not a quote.
Next steps
- Confirm thickness before you buy.
- Compare waste-adjusted yards against real bag count.
- If the bag count sounds miserable, call a supplier now.
Common mistakes
- Using the exact math result without a waste allowance.
- Choosing bags for a pour that is already truck-sized.
- Using the same thickness for every job type.
Use this page to plan the purchase, then confirm local pricing and delivery minimums before ordering.
1. Enter Dimensions
Length, width, and thickness of your slab.
Common: 4" (patio/walkway), 6" (driveway), 8" (heavy-duty)
Average ready-mix: $125-$150/yd³
Quick Presets
2. Results
Your concrete calculation.
Enter your project dimensions
Or use a quick preset to see an example calculation.
How Much Concrete for Common Projects
| Project | Size | Thickness | Cubic Yards | 80lb Bags | Est. Cost |
|---|---|---|---|---|---|
| Small Patio | 10×10 | 4" | 1.23 | 56 | $172 |
| Driveway Section | 10×10 | 6" | 1.85 | 84 | $259 |
| Medium Patio | 12×12 | 4" | 1.78 | 80 | $249 |
| Shed Foundation | 12×12 | 6" | 2.67 | 120 | $373 |
| Large Patio | 20×20 | 4" | 4.94 | 223 | $691 |
| 2-Car Garage | 24×24 | 6" | 10.67 | 480 | $1,493 |
| Walkway | 4×25 | 4" | 1.23 | 56 | $172 |
Cost estimates based on $140/yd³ for ready-mix. Actual prices vary by location.
How to Calculate Concrete for Any Project
The formula for calculating concrete is simple: Length × Width × Thickness = Volume. But the units matter. Here's how to get it right.
Step 1: Measure Your Project
Measure the length and width in feet. Measure the thickness in inches. Most residential slabs are 4 inches thick (patios, walkways) or 6 inches (driveways, garage floors).
Step 2: Calculate Cubic Feet
Cubic Feet = Length (ft) × Width (ft) × [Thickness (in) ÷ 12]
For a 10×10 slab at 4 inches thick: 10 × 10 × (4÷12) = 33.3 cubic feet
Step 3: Convert to Cubic Yards
Cubic Yards = Cubic Feet ÷ 27
For our 10×10 slab: 33.3 ÷ 27 = 1.23 cubic yards
Step 4: Add Waste Factor
Always order 10% more than calculated. This covers spillage, uneven ground, and slight measurement errors. For complex forms, use 15%.
Order Amount = Calculated Yards × 1.10
Step 5: Decide Ready-Mix vs Bags
Ready-Mix (Recommended for 1+ yd³)
- Delivered by truck
- $125-$150 per cubic yard + delivery
- Faster pour, better quality
- Minimum order usually 1 yard
Bags (For small projects)
- 80lb bag = 0.6 cubic feet (0.022 yd³)
- 60lb bag = 0.45 cubic feet
- $5-$7 per 80lb bag
- Good for under 1 cubic yard
Concrete Calculator Examples
10×10 Slab
4" thick: 1.23 yd³ (56 bags) | 6" thick: 1.85 yd³ (84 bags)
See full breakdown →
12×12 Slab
4" thick: 1.78 yd³ (80 bags) | 6" thick: 2.67 yd³ (120 bags)
See full breakdown →
20×20 Slab
4" thick: 4.94 yd³ (223 bags) | 6" thick: 7.41 yd³ (334 bags)
See full breakdown →
Custom Slab Size
Enter any dimensions for your project
Use slab calculator →