Updated · Built and checked by the PlinzoTools team, formulas tested against published sources
Size a concrete slab and see exactly how much to order from a ready-mix truck, rounded to the nearest 1/4 yard.
2.75 cu yd
Calculated volume (before rounding): 2.716 cu yd -- ready-mix is sold in 1/4 cu yd increments.
This tool sizes a rectangular concrete slab -- the same length × width × thickness math as the general Concrete Calculator -- but it's built specifically around ordering from a ready-mix truck rather than buying bags. Ready-mix suppliers don't sell arbitrary volumes; they sell in 1/4 cubic yard increments, so this calculator rounds your calculated volume up to the next quarter-yard, which is the number you actually give the dispatcher.
Pick a common slab thickness preset (4in for a patio or sidewalk, 5in for a garage slab, 6in for a driveway) or enter a custom thickness, then enter your slab's length and width in feet. The result shows both your calculated volume and the rounded order size.
Order (cu yd) = ROUNDUP(Calculated Volume × 4) ÷ 4
If your slab needs 1.63 cu yd of concrete, no supplier will deliver exactly 1.63 yards -- they'll round up to 1.75 cu yd, and you pay for that full 1.75. Ordering the raw, unrounded number and being surprised by the invoice is one of the most common first-time mistakes with a ready-mix delivery; this calculator shows you the real number up front.
Use this before calling a ready-mix supplier for any slab over roughly 1 cubic yard -- below that, bagged concrete (see the Concrete Bag Calculator) is usually more practical since most trucks have a minimum delivery load anyway. Once you know your order size, the Concrete Cost Calculator turns it into a material cost estimate using your supplier's actual quoted price.
Many ready-mix suppliers also charge a "short load" fee for orders below a minimum (commonly 3-5 cu yd, though this varies by region and supplier) -- always confirm minimums and any short-load fee with your supplier before ordering, since this calculator only sizes the concrete itself.
Take a garage slab 16 ft by 12 ft at 5 in thick. The raw volume is 16 × 12 × (5 ÷ 12) = 80 cubic feet, or about 2.96 cubic yards. Add a 10 percent waste allowance and the figure rises to about 3.26 cubic yards. Multiply by 4 to get 13.04, round up to 14, and divide by 4: the order size is 3.5 cubic yards. Notice that a small overage in the calculated volume can push you up a full quarter yard, so it is worth knowing which side of a boundary you are on before you phone the supplier.
3.26 × 4 = 13.04, rounded up to 14, then 14 ÷ 4 = 3.5 cu yd
Real pours use more than the theoretical volume because subgrade is rarely perfectly level, forms can bow slightly, and some material stays in the truck chute or spills. The allowance protects you against running short. Decide the percentage based on how uniform your base is; a carefully compacted, level base may justify less, and a rough or uncertain one more. Your concrete supplier or a local contractor can advise on a sensible margin for your conditions.
The tool does not choose a mix strength, reinforcement, control joint spacing or base depth. Those depend on how the slab will be used, your soil, and your local climate and building code, so confirm them with the supplier, a structural professional or your building department.
Concrete trucks and batching plants are set up to measure and mix in quarter-yard increments, so orders are placed and billed in those units rather than arbitrary decimals.
6 inches is standard for a residential driveway that needs to support vehicle weight, versus 4 inches for a patio or walkway that only carries foot traffic.
Running short mid-pour is a bigger problem than having a small amount left over, since a cold joint (where new concrete meets already-set concrete) can weaken the slab. The quarter-yard rounding already builds in a small safety margin.
Yes -- the same length x width x thickness math applies at any size; just be aware very large pours (drivable driveways, big patios) often need a short-load fee discussion with your supplier if under their minimum.
Round up. The calculator already does this to the next quarter yard, because a shortfall mid-pour is more costly than a small surplus.
For small volumes, yes. Bagged mix is practical below about a cubic yard, but larger slabs are usually more efficient from a truck. Compare a bag count with a delivery quote.
No. Enter only the thickness of the concrete itself. The gravel or sand base beneath it is a separate material and is not part of this volume.