Concrete Calculator
Ordering the right amount of concrete is critical — too little stops your project cold, too much wastes money. This concrete calculator figures out exactly how many cubic yards you need and how many 60-pound bags to buy for smaller jobs, based on your slab's length, width, and thickness.
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Formula
Volume (cu yd) = L × W × (T/12) / 27
L is length in feet, W is width in feet, T is thickness in inches (divided by 12 to convert to feet), and the result is divided by 27 to convert cubic feet to cubic yards. One cubic yard fills about 45 60-lb bags.
How to use the Concrete Calculator
- 1
Enter your length (ft)
Value should be in ft.
- 2
Enter your width (ft)
Value should be in ft.
- 3
Enter your thickness (in)
Value should be in in.
- 4
Read your results instantly
Results update in real time as you type.
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When to Order Ready-Mix vs. Bags
For slabs under about 1 cubic yard (roughly a 10×10 ft area at 4 inches thick), bagged concrete mixed on-site is often more economical. For larger pours, ready-mix delivered by truck is faster, more consistent, and generally less expensive per yard. Ready-mix typically comes in minimum loads of 1 yard, so plan your project carefully to avoid paying for a partial load.
Standard Concrete Thickness Guidelines
Sidewalks and patios are typically 4 inches thick. Driveways should be 4–6 inches. Structural footings are often 8–12 inches depending on local code and load requirements. A 4-inch slab is the most common residential pour and the default in this calculator. Always check your local building codes before setting final thickness.
Tips & Insights
Order 10% Extra
Always order 5–10% more concrete than your calculation to account for spillage, uneven subgrade, and form bulge. Running short mid-pour creates cold joints that weaken the slab.
Compact the Subgrade First
A properly compacted and leveled gravel base reduces concrete settling and cracking. Skipping this step wastes concrete filling voids and leads to an uneven slab.
Check the Weather
Avoid pouring concrete when temperatures are below 40°F or above 90°F. Extreme cold slows curing; extreme heat causes premature drying and surface cracking.
Worked Examples
Backyard Patio Slab
2.47 cubic yards — order 3 yards from a ready-mix supplier to have a small buffer.
Garden Path
1.04 cubic yards — approximately 47 bags of 60-lb concrete mix.
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Frequently Asked Questions
How many 60-lb bags of concrete make a cubic yard?
It takes approximately 45 bags of 60-lb premix concrete to fill one cubic yard.
How thick should a concrete driveway be?
Residential driveways are typically 4 inches thick for standard vehicles. For heavy trucks or RVs, 5–6 inches is recommended.
How long does concrete take to cure?
Concrete reaches about 70% of its strength in 7 days and full design strength in 28 days. You can walk on it after 24–48 hours but avoid vehicle traffic for at least 7 days.
What is a cubic yard of concrete?
A cubic yard is 27 cubic feet (3 ft × 3 ft × 3 ft). It weighs approximately 4,000 pounds (2 tons).
Can I add water to bagged concrete to make it easier to mix?
Follow the water ratio on the bag exactly. Too much water weakens the finished concrete significantly — each extra pound of water per bag can reduce strength by up to 200 psi.
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