How much concrete do I need for a slab?
Multiply the slab's length and width in feet by its thickness in feet (thickness in inches ÷ 12), which gives cubic feet. Divide by 27 to get cubic yards, then add a waste factor — typically 10% — before ordering. This calculator does that conversion for you and also converts the result into 40, 60, and 80 lb bag counts.
How many bags of concrete do I need?
Divide your waste-adjusted volume in cubic feet by the bag's mixed yield: about 0.30 ft³ for a 40 lb bag, 0.45 ft³ for a 60 lb bag, or 0.60 ft³ for an 80 lb bag, then round up. These yields are printed on Quikrete's and Sakrete's own technical data sheets and are identical across both manufacturers.
How many cubic feet are in a cubic yard of concrete?
27 cubic feet (3 ft × 3 ft × 3 ft). Ready-mix concrete is ordered and priced by the cubic yard, so this is the conversion that turns a raw volume calculation into an order quantity.
Why does the calculator add a waste factor?
NRMCA's official guidance for ordering ready-mix (CIP 31) recommends ordering 4–10% more than the plan-dimension estimate to cover spillage, an uneven subgrade, and overfilling forms during placement. This calculator defaults to 10%, the top of that range, and lets you adjust it.
Should I buy bags or order ready-mix?
Pre-mix bags are practical for small jobs, generally under about 1–2 cubic yards. Past that, ready-mix delivered by truck is usually more economical and far less physical work than mixing dozens of bags by hand — though many suppliers apply a minimum order or a short-load fee below roughly a cubic yard, so it’s worth calling ahead.
How thick should a concrete slab be?
Common residential figures are 4 inches for patios and walkways and 6 inches for driveways, with 8–12 inches for slabs carrying heavy equipment — but local building codes can set their own minimums, so check before pouring anything load-bearing or permitted.
Do I need to account for rebar or wire mesh in my order?
No — reinforcement displaces a negligible amount of concrete and is normally ignored when estimating volume. Order the full calculated amount; the steel sits inside the pour rather than reducing how much concrete you need.
What's the difference between a slab, a footing, and a column in this calculator?
A slab and a footing use the identical rectangular formula — length × width × depth — since a footing is really just a narrow trench of concrete; there's no separate manufacturer-published "footing formula." A column or post uses the circular formula, π × radius² × depth, based on the diameter you enter.
Is there a minimum order for ready-mix concrete trucks?
Often, but it's not a fixed universal rule. Many regional ready-mix plants use around a 1 cubic yard minimum with a short-load surcharge below that, some suppliers advertise no minimum on volumetric mixer trucks, and others set baseline minimums of 3–4+ cubic yards. Always confirm the minimum and any short-load fee with your specific local plant.