Concrete Calculator
Estimate the cubic yards, bags, and cost of concrete for slabs, footings, columns, and walls. Includes a 10% waste factor and side-by-side comparison of ready-mix versus bag pricing.
How the concrete calculator works
The underlying math is simple: length × width × depth, converted into cubic yards (one cubic yard equals 27 cubic feet). What separates a useful estimate from a frustrating one is the accounting — the waste factor, the unit conversions, and a realistic bag-yield number.
We assume a 60-lb bag yields roughly 0.45 ft³ of mixed concrete and an 80-lb bag yields 0.60 ft³. These are manufacturer averages; your actual yield will vary by 5–10% depending on water content and aggregate.
When to pour thicker than 4 inches
A 4″ slab is the default for patios, walkways, and shed pads. Step up to 5″ for standard driveways, 6″ for driveways that see trucks or trailers, and 8–12″ for footings, depending on local code and soil bearing.
- 4″ — patios, walkways, sheds
- 5–6″ — driveways, garage floors
- 8–12″ — footings, retaining walls
Getting the order right
Ready-mix suppliers sell in ¼-yard increments with a short-load fee under 3–4 yd³. Call two days ahead, confirm the truck's reach, and have your forms, rebar, and finishing tools on site before the truck arrives. Hot weather? Ask for a retarder. Cold? Ask for an accelerator.
Sources
- Standard concrete density: 150 lb/ft³
- Bag yields per manufacturer averages (Quikrete, Sakrete)
- Average ready-mix price: $165/yd³ delivered (ENR, 2026)