How Much Concrete Do I Need? (Quick Answer + Calculator)
A **10×10 slab at 4 inches thick needs 1.2 cubic yards** (about 55 bags of 80-lb concrete). A **12×12 patio needs 1.8 cubic yards** (about 80 bags). Check the reference table below for common sizes, or use our [concrete calculator](/calculators/concrete-calculator) for your exact dimensions.
How Much Concrete Do I Need? (Quick Answer + Calculator)
A 10×10 slab at 4 inches thick needs 1.2 cubic yards (about 55 bags of 80-lb concrete). A 12×12 patio needs 1.8 cubic yards (about 80 bags). Check the reference table below for common sizes, or use our concrete calculator for your exact dimensions.
Quick Reference Table
Here are concrete quantities for common project sizes at standard thicknesses:
Patios and Slabs (4" thick)
| Size | Cubic Yards | 80-lb Bags |
|---|---|---|
| 8×8 ft | 0.8 | 36 |
| 10×10 ft | 1.2 | 55 |
| 10×12 ft | 1.5 | 67 |
| 12×12 ft | 1.8 | 80 |
| 12×14 ft | 2.1 | 93 |
| 14×14 ft | 2.4 | 108 |
| 16×16 ft | 3.2 | 142 |
| 20×20 ft | 4.9 | 222 |
Driveways (5" thick)
| Size | Cubic Yards | 80-lb Bags |
|---|---|---|
| 10×20 ft | 1.5 | 70 |
| 12×20 ft | 1.9 | 83 |
| 16×20 ft | 2.5 | 111 |
| 20×20 ft | 3.1 | 139 |
| 20×24 ft | 3.7 | 167 |
| 24×24 ft | 4.4 | 200 |
| 20×40 ft | 6.2 | 278 |
Sidewalks (4" thick, 3 ft wide)
| Length | Cubic Yards | 80-lb Bags |
|---|---|---|
| 10 ft | 0.37 | 17 |
| 20 ft | 0.74 | 34 |
| 30 ft | 1.1 | 50 |
| 40 ft | 1.5 | 67 |
| 50 ft | 1.9 | 83 |
Note: All quantities include a 10% waste buffer. Round up when ordering.
For custom dimensions, use our slab calculator or patio calculator.
Standard Thickness by Project
These recommendations affect how much concrete you need:
| Project | Recommended Thickness |
|---|---|
| Patio | 4 inches |
| Sidewalk | 4 inches |
| Shed pad | 4 inches |
| Driveway (cars) | 5 inches |
| Driveway (trucks/RV) | 6 inches |
| Garage floor | 4-6 inches |
Using the wrong thickness is a common mistake. A patio at 4" uses 25% less concrete than the same size at 5". But a driveway at 4" will crack under vehicle weight—don't cut corners to save concrete.
How to Calculate Your Own
If your project isn't in the tables, here's the quick formula:
Cubic yards = Length (ft) × Width (ft) × Thickness (ft) ÷ 27
Thickness conversion:
- 4 inches = 0.33 feet
- 5 inches = 0.42 feet
- 6 inches = 0.50 feet
Example: 15×11 patio at 4"
- 15 × 11 × 0.33 = 54.5 cubic feet
- 54.5 ÷ 27 = 2.0 cubic yards
- Plus 10% waste = 2.2 cubic yards
For a full walkthrough with examples, see how to calculate concrete.
Bags vs Ready-Mix: When to Use Each
Your quantity determines whether to buy bags or order delivery:
| Cubic Yards | 80-lb Bags | Recommendation |
|---|---|---|
| Under 0.5 | Under 25 | Bags |
| 0.5-1.0 | 25-45 | Bags |
| 1.0-1.5 | 45-70 | Either (bags if DIY) |
| 1.5-2.0 | 70-90 | Lean toward ready-mix |
| Over 2.0 | 90+ | Ready-mix |
Why the threshold matters:
- One person can reasonably mix 20-30 bags in a day
- Ready-mix has minimum orders (usually 1 yard) and short-load fees
- Mixing 80+ bags by hand is exhausting and time-consuming
For a detailed comparison, see ready-mix vs bagged concrete.
Coverage Per Cubic Yard
One cubic yard covers different areas depending on thickness:
| Thickness | Coverage per Yard |
|---|---|
| 3 inches | 108 sqft |
| 4 inches | 81 sqft |
| 5 inches | 65 sqft |
| 6 inches | 54 sqft |
Practical use: If you're ordering 3 yards of concrete at 4" thick, you can cover approximately 243 square feet (3 × 81).
Always Order Extra
The quantities in this guide include a 10% buffer, but consider ordering slightly more if:
- Your ground is uneven (low spots use more concrete)
- You're new to concrete work (mistakes happen)
- The project has complex shapes
- You'd rather have excess than run short
Running short mid-pour is a serious problem. You can't stop, order more concrete, and continue tomorrow—the joint between old and new concrete will be a weak point. Having a little leftover is far better.
What About Post Holes?
For fence posts, mailbox posts, and similar holes:
| Hole Size | Depth | Concrete Needed |
|---|---|---|
| 8" diameter | 24" | 0.5-1 bag per hole |
| 10" diameter | 30" | 1-2 bags per hole |
| 12" diameter | 36" | 2-3 bags per hole |
For posts, use fast-setting concrete—it's formulated for this application and sets in 20-40 minutes.
Common Questions
How many bags of concrete for a 10×10 slab?
At standard 4-inch thickness: approximately 55 bags of 80-lb concrete (or 1.2 cubic yards of ready-mix). This includes a 10% waste buffer.
How much does a yard of concrete cover?
One cubic yard covers 81 square feet at 4 inches thick, 65 square feet at 5 inches, or 54 square feet at 6 inches. Thicker slabs cover less area with the same volume.
Should I get bags or ready-mix?
For projects under 1 cubic yard (about 45 bags), bags are practical. For projects over 1.5 cubic yards, ready-mix saves significant time and labor. See our comparison guide for details.
Frequently Asked Questions
How many bags of concrete for a 10×10 slab?
Approximately 55 bags of 80-lb concrete for a 10×10 slab at 4 inches thick, including 10% extra for waste. That's about 1.2 cubic yards if ordering ready-mix.
How much does a yard of concrete cover?
At 4 inches thick, one cubic yard covers about 81 square feet. At 5 inches, it covers 65 square feet. At 6 inches, 54 square feet. Thickness is the variable that determines coverage.
Should I get bags or ready-mix?
Use bags for projects under 1 cubic yard (45 bags). Use ready-mix for anything over 1.5 cubic yards. In between, consider how much manual labor you're willing to do—mixing 60+ bags is hard work.
Key Takeaways
- 10×10 patio (4"): 1.2 cubic yards / 55 bags
- 12×12 patio (4"): 1.8 cubic yards / 80 bags
- 20×20 driveway (5"): 3.1 cubic yards / 139 bags
- Always include 10% waste buffer
- Use bags under 1 yard, ready-mix over 1.5 yards
Use our concrete calculator for exact quantities. Make sure you know the difference between concrete and cement when shopping. For more guidance, see how many bags you need or browse all concrete guides.