Concrete Calculator

How much concrete do I need for a 10×10 slab?

For a 10×10 foot slab that is 4 inches thick, you need approximately 1.23 cubic yards of concrete without waste, or 1.36 cubic yards with 10% waste added. That is about 62 bags of 80lb concrete mix, or 82 bags of 60lb mix. The exact amount depends on your slab thickness — standard residential slabs are 4 inches thick, while driveways and garage floors are typically 5-6 inches.

How many bags of concrete do I need per cubic yard?

One cubic yard of concrete equals 27 cubic feet. You need approximately 45 bags of 80lb concrete mix, 60 bags of 60lb mix, or 90 bags of 40lb mix to make one cubic yard. For projects larger than 1-2 cubic yards, ordering ready-mix concrete from a local supplier is usually more cost-effective than buying bags.

How thick should a concrete slab be?

Standard residential concrete slab thickness depends on the use: sidewalks and patios are typically 4 inches thick, driveways should be 5-6 inches, and garage floors are usually 4-6 inches. For heavy vehicle traffic or commercial use, 6-8 inches or more may be required. Always check local building codes for minimum requirements.

How do you calculate concrete in cubic yards?

To calculate concrete in cubic yards: (1) Measure length and width in feet, (2) Measure thickness in inches, (3) Convert thickness to feet by dividing by 12, (4) Multiply length × width × thickness (in feet) to get cubic feet, (5) Divide by 27 to convert to cubic yards. For example: 10 ft × 10 ft × (4 in ÷ 12) = 33.33 cu ft ÷ 27 = 1.23 cubic yards.

What is the waste factor and how much should I add?

The waste factor accounts for concrete lost to spillage, uneven ground, over-excavation, and form imperfections. The industry standard is 5-10% for simple rectangular pours and 10-15% for irregular shapes or rough terrain. This calculator defaults to 10%, which is sufficient for most residential projects.

How much does concrete cost per cubic yard?

Ready-mix concrete typically costs $100-$200 per cubic yard depending on your location, mix strength, and delivery distance. Bagged concrete (80lb bags) costs approximately $5-7 per bag, which works out to $225-$315 per cubic yard. For small projects under 1 cubic yard, bags are convenient; for larger projects, ready-mix delivery is more economical.

How do I calculate concrete for a round column or post?

For cylindrical columns: Volume = π × (diameter/2)² × height. Convert diameter to feet first (divide inches by 12). For example, a 12-inch diameter column that is 4 feet deep: π × (0.5)² × 4 = 3.14 cubic feet = 0.12 cubic yards. Multiply by the number of columns and add your desired waste percentage.

What is the difference between concrete and cement?

Cement is an ingredient in concrete — it is the binding powder (Portland cement) that holds everything together. Concrete is the finished product made by mixing cement with water, sand (fine aggregate), and gravel (coarse aggregate). When you buy a "bag of concrete," it contains pre-mixed cement, sand, and gravel — you just add water.