Concrete Calculator
Cubic yards of ready-mix to order — or bags to buy — for slabs, footings, and post holes, with a waste allowance so you never run short mid-pour.
Concrete is sold by the cubic yard for ready-mix and by the bag for small jobs, and the volume math trips people up because thickness is in inches while the footprint is in feet. This calculator handles the conversion for slabs, footings, and round post holes, scales by quantity, and adds waste.
Planning a patio? Pair it with the Room Planner to set the footprint and the Renovation Budget for the full project, and read outdoor patio planning.
FAQ
- How much concrete do I need?
- Volume is length × width × thickness, converted to cubic yards (1 yard = 27 cubic feet). This tool computes it for slabs, footings, and round post holes, multiplies by quantity, and adds a waste allowance for spillage and uneven subgrade.
- Bags or ready-mix?
- Order ready-mix by the cubic yard for anything over about half a yard — bags get expensive and labor-intensive fast. Bags (40, 60, or 80 lb) make sense for small jobs like a few post holes or a small pad.
- Why round up?
- A concrete pour can't be paused to run to the store — if you come up short on a slab, the cold joint is a permanent weak point. Always order a little extra; leftover is far cheaper than a failed pour.
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