Concrete Calculator

Ordering the right amount of concrete saves money and avoids project delays. Too little means a second pour with a visible cold joint; too much is wasted material. This calculator handles the geometry so you can focus on the project.

Slab thickness guide: Sidewalks and patios typically need 4 inches. Driveways and garage floors need 5–6 inches. Heavy equipment pads and commercial floors may require 6–8 inches or more. Always check local building codes for your specific application.

Always add a waste factor: Concrete is hard to order precisely. Uneven subgrade, form bulges, and spillage all consume extra material. A 5–10% overage is standard practice. For complex shapes or stairs, use 10–15%.

Bag yields: A 40-lb bag yields about 0.011 cubic yards (0.30 cu ft). A 60-lb bag yields about 0.017 cubic yards (0.45 cu ft). An 80-lb bag yields about 0.022 cubic yards (0.60 cu ft). For anything over 1–2 cubic yards, consider ordering ready-mix delivery — it's more cost-effective and much faster.

Ready-mix vs. bags: Bagged concrete typically costs $5–8 per 80-lb bag ($150–240 per cubic yard). Ready-mix delivery runs $120–180 per cubic yard for the concrete itself, plus a delivery fee. The crossover point is usually around 1–2 cubic yards.

Subgrade preparation: Good concrete starts below the surface. Compact the soil, add 4–6 inches of gravel base for drainage, and use forms to contain the pour. A proper subgrade prevents cracking and settling.

Curing time: Concrete reaches about 70% of its strength in 7 days and full strength (typically 4,000 PSI) in 28 days. Keep it moist during the first week for best results.