Calculate the exact amount of concrete needed for slabs, footings, columns, and more.
How much concrete for a 10x10 slab? A 10x10 slab at 4 inches thick requires about 1.23 cubic yards of concrete (1.35 yards with 10% waste). That's about 61 80-lb bags if mixing yourself. For a 12x12 slab at 4 inches, you'd need about 1.78 cubic yards.
Calculating concrete accurately is crucial-order too little and you'll delay work; order too much and you waste money and material. In practice, most people underestimate by 10-15% because they forget about spillage, over-excavation, and uneven subgrades. Our concrete calculator uses industry-standard formulas to give you precise estimates for slabs, footings, columns, and more. Whether you're pouring a small patio, building a foundation, or setting posts, this tool accounts for waste factors (typically 5-10%), converts between yards, feet, and bags, and even helps you decide between ready-mix and bagged concrete. Built with feedback from professional contractors, it's trusted for both DIY projects and commercial jobs. Start by entering your dimensions below, and we'll calculate everything from cubic yards to the number of 60-lb bags you'll need.
Take accurate measurements of your slab, footing, or column dimensions. Use a tape measure and record measurements in feet, inches, or meters.
Input the length, width, and thickness for slabs, or diameter and depth for footings, or width, length, and height for columns.
Choose the appropriate unit for each measurement. The calculator will automatically convert between units.
Include a waste factor (typically 5-10%) to account for spillage, over-excavation, and irregularities.
Click "Calculate Concrete Needs" to get your results in cubic yards, cubic feet, and bags.
See exactly how much concrete you need for common projects. Each example shows cubic yards, 80-lb bag counts, and pro tips for ordering. Use these real-world calculations to plan your project, then enter your own dimensions in the calculator above.
Dimensions: 10 ft x 10 ft x 4 in thick
Tip: For slabs over 1 yd³, order ready-mix concrete instead of bags-it's cheaper and faster. This project is borderline; compare bagged vs. ready-mix costs.
Dimensions: 12 ft x 20 ft x 4 in thick
Tip: At nearly 3.3 cubic yards, ready-mix concrete is the only practical choice. Order 3.5 yards to allow for spillage and uneven subgrade.
Dimensions: 20 ft x 20 ft x 6 in thick
Tip: This size requires a ready-mix truck. Order 8.5 yards to be safe, and schedule the pour for early morning to avoid afternoon heat.
Dimensions: 12-in diameter x 24 in deep x 6 holes
Tip: Bagged concrete is ideal for post holes. Mix one bag per hole for consistency, and consider using fast-setting concrete for quicker installation.
Dimensions: 12-in diameter x 36 in deep x 6 footings
Tip: Use sonotubes for clean, consistent footings; order extra for over-digging. For frost-depth footings, verify local code requirements.
Dimensions: 12-ft diameter x 4 in thick
Tip: Circular slabs need careful forming; add 15% waste for irregular edges. Consider ordering 1.75 yards of ready-mix for easier placement.
Note: These examples assume standard densities and include typical waste factors. 80-lb bag yields about0.6 ft³ of concrete. Your exact needs may vary based on site conditions and material choices. Always round up when ordering.
Determining concrete quantity depends on three factors: length, width, and thickness. Here's a simple rule of thumb:
Cubic Yards = (Length (ft) x Width (ft) x Thickness (in) / 12) / 27
Add 5-10% for waste, and round up to the nearest 1/4 yard when ordering ready-mix.
For common slab sizes at 4 inches thick (standard for patios and sidewalks):
| Slab Size | Area (sq ft) | Cubic Yards | 80-lb Bags Needed |
|---|---|---|---|
| 10x10 | 100 | 1.23 | 61 |
| 12x12 | 144 | 1.78 | 89 |
| 15x15 | 225 | 2.78 | 139 |
| 20x20 | 400 | 4.94 | 247 |
| 10x20 | 200 | 2.47 | 124 |
| 12x24 | 288 | 3.56 | 178 |
Note: Based on 4-inch thickness, no waste factor included. Add 5-10% extra for waste. 1 cubic yard about 81 sq ft at 4 inches thick.
Bagged Concrete (40-90 lb bags): Best for small projects under 1 cubic yard. Easy to handle, no minimum order, but more expensive per yard and labor-intensive.
Ready-Mix Concrete (truck delivery): Cost-effective for projects over 1 cubic yard. Requires scheduling, access for the truck, and faster placement.
Our calculator automatically compares bagged and ready-mix options based on your project size.
Choosing the right concrete thickness is critical for durability and load-bearing capacity. The table below summarizes recommended thicknesses for common applications, based on industry standards and building codes.
Always check local building codes for specific thickness requirements in your area. When in doubt, consult a structural engineer.
Need to calculate material for your thickness? Use our concrete calculator above, or explore gravel calculator for base material needs.
Understanding concrete costs helps you budget accurately. Prices vary by region, project size, and concrete mix, but these estimates will give you a realistic range for planning.
| Material | Price Range | Typical Use |
|---|---|---|
| Ready-Mix Concrete | $120-$200 per cubic yard | Slabs, driveways, foundations (4+ yards) |
| 80-lb Bagged Concrete | $5-$7 per bag | Small projects, post holes, repairs (<1 yard) |
| High-Strength Mix (4000+ psi) | $140-$220 per yard | Driveways, garage floors, commercial |
| Fiber-Reinforced Concrete | $150-$230 per yard | Driveways, industrial floors |
Total Cost about (Cubic Yards x Price per Yard) + Delivery + Labor + Reinforcement
Example: A 10x20 slab (4" thick) = 2.47 yards x $160/yard = $395 for concrete + $100 delivery + $600-$1200 labor = about$1,100-$1,700 total.
Pro Tip: Get quotes from 2-3 local suppliers. Prices can vary 20-30% between companies. Ask about weekend delivery surcharges and minimum order requirements.
Calculate your exact concrete needs with our concrete calculator, then use these cost ranges to budget your project. For base materials, see our gravel calculator for driveway and patio base costs.
Choosing between bagged and ready-mix concrete affects cost, labor, and project success. This guide helps you make the right choice based on your project size, access, and budget.
Best for projects under 1 cubic yard
When to choose: Projects <1 yard, difficult access, weekend work, small batches needed over time.
Best for projects over 1 cubic yard
When to choose: Projects >1 yard, good truck access, professional or experienced DIY installers.
A 10x10 slab (4" thick) requires 1.35 cubic yards with waste:
Savings with Ready-Mix: $170 (35% less). Plus, ready-mix saves 6-8 hours of mixing labor.
Pro Tip: Our concrete calculator automatically shows both bagged and ready-mix quantities. For projects between 0.5-1.5 yards, calculate both options and compare total cost including your labor time. For detailed bag calculations, see our concrete bag calculator guide.
Need base material? Check our gravel calculator for driveway and patio base requirements, or our paver calculator for hardscape projects that might use concrete as a base. For detailed pricing information, see our concrete cost estimator guide.
Avoid these frequent errors that lead to costly over-orders or dangerous shortages:
Concrete spills, forms leak, and subgrades can be uneven. Always add 5-10% extra volume. For DIYers, 10% is a safe buffer.
Mixing units (e.g., entering thickness in feet instead of inches) can cause a 12x error! Double-check your units before calculating.
There are 27 cubic feet in a cubic yard. Many DIYers order concrete in cubic feet, then wonder why they're short by a factor of 27.
Footings must extend below the frost line (often 36+ inches). Check local building codes for required depths.
Rebar and wire mesh displace concrete. For heavily reinforced slabs, add 3-5% extra concrete to account for displacement.
Pro Tip: Use our calculator's waste-factor field and unit-conversion features to avoid these mistakes automatically.
Professional contractors know that standard calculations only get you partway-real jobsites demand practical adjustments. Here's what the pros consider beyond the numbers:
Real contractors have seen these scenarios play out hundreds of times-here's what actually happens when estimates are wrong:
Most people underestimate by 10-15%. If your ground is soft, double the base depth. If you're on a slope, use the deepest point for calculations, not average. When the forecast says rain, delay the pour-wet concrete diluted by rain is weak concrete. If you're between truck sizes, order the larger one-it's cheaper than a second load.
Bottom line: Use the calculator for the baseline, then adjust for your specific site conditions. When in doubt, over-order-it's cheaper to have a little extra than to run short. But be smart about it: 5-10% extra is insurance; 30% extra is waste.
Standard concrete calculations assume a flat, stable, rectangular site. Real projects often diverge-here's how to adjust your estimate for common curveballs.
Remember: These adjustments are why contractors always order extra. Use the calculator to get your baseline, then layer on these real-world factors for a bulletproof estimate.
While our calculator provides accurate estimates for planning and material ordering, there are situations where professional input is essential:
The bottom line: Use this calculator for material estimates on typical residential projects (patios, walkways, simple slabs). For anything structural, complex, or commercial-consult a licensed professional. The calculator gives you numbers to discuss with your contractor, not a substitute for engineering judgment.
Insights from professional contractors to ensure your concrete projects go smoothly:
These tips, combined with our accurate calculator, will help you order the right amount of concrete the first time-saving money, time, and frustration.
One cubic yard of concrete equals 27 cubic feet. This is enough to cover an area of 81 square feet at 4 inches thick, or 108 square feet at 3 inches thick.
It depends on the bag size:
Cubic feet is a smaller unit. There are 27 cubic feet in one cubic yard. Most ready-mix concrete suppliers measure in cubic yards, while bagged concrete is often measured in cubic feet.
Typical thicknesses:
Yes, always order 5-10% extra concrete to account for spillage, over-excavation, and variations in subgrade. It's better to have a little extra than to run short.
Concrete reaches about 70% of its strength after 7 days and full strength after 28 days. However, you can walk on it after 24-48 hours, drive on it after 7 days, and place heavy loads after 28 days. Curing time depends on temperature, humidity, and mix design.
Concrete costs vary by region and project size. As of 2026, typical prices range from $120 to $200 per cubic yard for ready-mix concrete. Additional costs include delivery fees ($60-$150), pumping fees ($300-$500 if needed), and labor. Bagged concrete costs more per yard ($200-$300) but has no delivery minimums.
Yes, but special precautions are needed below 40°F (4°C). Use insulated blankets or heated enclosures, add accelerators to the mix, and ensure the ground isn't frozen. Concrete should not be poured on frozen ground or when temperatures are below 25°F (-4°C) without professional heating systems.
For irregular shapes, break the area into regular shapes (rectangles, triangles, circles), calculate each separately, then sum the volumes. Our calculator supports rectangular and circular areas. For complex shapes, consider adding 15-20% waste factor to account for difficult forming and uneven excavation.