Free Concrete Calculator
Calculate cubic yards, bags needed, and total cost for any concrete project — slabs, footings, columns, walls, stairs & more.
Frequently Asked Questions
How much concrete do I need for a 10×10 slab?
For a 10×10 slab at 4 inches thick: 10 × 10 × 0.333 = 33.3 cubic feet ÷ 27 = 1.23 cubic yards. That's about 56 bags (80 lb) or roughly $185 for ready-mix delivery. Always add 5-10% for waste.
How many bags of concrete are in a cubic yard?
Approximately 45 bags (80 lb), 60 bags (60 lb), or 90 bags (40 lb) per cubic yard. Yields vary by brand — always check the bag label.
How much does a yard of concrete weigh?
One cubic yard of concrete weighs approximately 4,050 pounds (about 2 tons). This equals 150 lb per cubic foot × 27 cubic feet per yard.
Should I use bags or ready-mix?
Bags: Best for small projects (under 1 cubic yard). More expensive per yard but no delivery minimum. Ready-mix: Best for jobs over 1 yard. Cheaper per yard ($125-$175/yd³ delivered) but usually requires a minimum order of 1+ yard.
How long does concrete take to cure?
Concrete sets in 24-48 hours (walkable), gains driving strength at 7 days, and reaches full strength at 28 days. Keep it damp during the first week for best results. Ideal pouring temperature is 50-70°F.
What is the concrete formula?
Rectangular: Volume (cu yd) = Length (ft) × Width (ft) × Depth (ft) ÷ 27
Round: Volume (cu yd) = π × Radius² (ft) × Depth (ft) ÷ 27
Remember: Convert inches to feet first by dividing by 12.
How to Use the Concrete Calculator
Our free concrete calculator helps contractors, DIYers, and homeowners estimate exactly how much concrete they need for any project. Simply select a shape, enter your dimensions, and get instant results in cubic yards, cubic feet, and number of bags — all in real time with no page reloads.
Step-by-Step Guide
- Select your shape — Choose from 9 shapes: slab, round slab, wall, footing, column, round column, tube, stairs, or curb & gutter.
- Enter dimensions — Type in length, width, and depth. You can switch between feet, inches, yards, meters, or centimeters.
- Set quantity — If you have multiple identical elements (e.g., 6 porch piers), set the quantity to avoid calculating each one separately.
- Add waste % — We recommend 5-10% extra for spillage, uneven surfaces, and over-excavation.
- Read results — See total cubic yards, weight in pounds, and exact bag counts for 40 lb, 50 lb, 60 lb, and 80 lb bags.
Recommended Concrete Thickness
Different projects require different slab thicknesses. Here are common starting points:
- Sidewalks: 4 inches
- Patios: 4 inches
- Driveways: 4-6 inches
- Garage floors: 4-6 inches
- Foundation footings: 8-12 inches
- Retaining walls: 6-8 inches
Understanding Concrete Measurements
Concrete is sold in two ways: by the bag (for small projects) and by the cubic yard via ready-mix delivery trucks (for larger projects). One cubic yard equals 27 cubic feet — enough to pour a 10×10-foot slab at about 4 inches thick.
When ordering ready-mix, always round up and order slightly more than calculated. Running short mid-pour is costly because you'll need another delivery, and the cold joint where old and new concrete meet can be a structural weakness.