Concrete Calculator

1. Select your shape. Choose Slab for flat poured areas like driveways, patios, and floors. Choose Column for solid round piers and footings. Choose Tube for hollow cylindrical forms like Sonotube deck footings.
2. Enter dimensions. For a slab, enter length and width in feet and depth in inches. A standard residential driveway slab is 4 inches deep. Sidewalks are typically 4 inches, garage floors 4 to 6 inches. For columns, enter the diameter in inches and height in feet. For tube forms, enter both outer and inner diameters so only the wall volume is counted.
3. Read cubic yards first. Ready-mix concrete is ordered by the cubic yard. If your project needs more than about 0.5 cubic yards (roughly 30 cubic feet), ordering ready-mix is almost always more cost-effective than buying bags.
4. Use bag counts for smaller pours. The calculator shows both 60 lb and 80 lb bag counts. A 10% waste factor is already included, which accounts for ground irregularities and spillage. Always round up to whole bags when purchasing.

Example: a 10 ft x 12 ft patio slab at 4 inches deep needs 40 cubic feet net, or about 1.63 cubic yards with waste. That is 98 bags of 60 lb concrete. At that volume, calling a ready-mix supplier saves money and labor.

Concrete volume is always calculated in cubic feet first, then converted to cubic yards for ordering ready-mix. The 10% waste factor covers settling, uneven subgrade, and overpour.

Concrete strength is measured in PSI. Standard residential slabs use 3,000 PSI mix. High-traffic driveways benefit from 4,000 PSI. Structural footings typically require 3,000 to 4,000 PSI per local building codes. When ordering ready-mix, specify the PSI rating, slump (workability), and whether you need air-entrained mix for freeze-thaw climates.