Estimate the cost of a concrete slab, pad, floor or footing from its dimensions and your own price per cubic yard. Volume and bag count are calculated; you supply the rate.
| Input | Result |
|---|---|
| 20 × 20 ft, 4 in, at $150/yd³, 10% waste | 5.43 yd³ · 223 bags · $814.81 |
| 12 × 24 ft, 6 in, at $150/yd³, 10% waste | 5.87 yd³ · 240 bags · $880 |
| 10 × 10 ft, 4 in, at $165/yd³, 5% waste | 1.3 yd³ · 56 bags · $213.89 |
The volume of a slab is exact: length times width times thickness, converted to cubic yards. There is no estimate in it, and any calculator will give you the same number from the same measurements. The cost is a different kind of quantity, because the rate is set locally.
Ready-mix concrete is priced per cubic yard delivered, and that rate moves with cement and aggregate costs, fuel surcharges, distance from the plant, and how big the order is. Two suppliers in the same city can differ noticeably, and a pour smaller than a full truckload almost always carries a short-load fee that dominates the arithmetic on small jobs. That is why the price field here is empty: the honest number is the one on your supplier’s quote.
Two items are easy to forget and are not in the yardage arithmetic. A base of compacted gravel under the slab, and reinforcement, wire mesh or rebar, both of which are ordered separately and priced separately. Add them to your own take-off before you call for a quote.
It depends almost entirely on two things you have to supply yourself: how many cubic yards the slab is, and what ready-mix costs per yard where you live. The yardage is exact arithmetic from your dimensions, this page calculates it. The price per yard is not something any website can know for your job; call two local ready-mix plants and ask for their delivered price per cubic yard, including any short-load fee for small pours.
Because ready-mix pricing varies by region, by season, by fuel surcharge and by order size, and the spread between markets is wide. Printing one national average would look authoritative and be wrong for most readers. Ask your supplier, and note that orders below a truckload usually carry a short-load surcharge that changes the effective rate a lot on small jobs.
Four inches is typical for sheds, patios and walkways; six inches for driveways and garage floors that carry vehicles. Thickness is set by what the slab has to carry and by your local code, so confirm against your building department's requirements rather than a rule of thumb.
No. Sub-grade is never perfectly flat, forms bow, and some material is lost in placement. Ordering roughly ten percent over the calculated volume is normal trade practice, which is why the waste field defaults to 10.
One cubic yard is 27 cubic feet, and an 80 lb bag yields 0.60 cubic feet, so a yard is 45 bags. For small jobs bagged mix avoids the short-load fee; for anything over roughly a yard, delivered ready-mix is usually cheaper per cubic foot.