How much does a concrete slab cost?
Multiply the slab's volume by your supplier's price, then add delivery and anything else you pay once, such as forms or rental tools. Prices vary widely by region and supplier, so this page does not publish them: enter the figures from your own quotes and the calculator does the arithmetic.
cost = cubic yards × price per yard + fixed costs
For bagged concrete, the volume becomes a bag count first. An 80 lb bag of standard mix yields about 0.60 cubic feet,[1] so a 10 × 10 ft slab 4 inches thick (33.3 cu ft) takes 56 bags, and its cost is 56 × your bag price.
Concrete cost per yard
A cubic yard costs your supplier's price per yard, plus any delivery or short-load charge they add. In bags, one cubic yard is 45 bags of 80 lb mix,[1] so the bagged cost of a yard is 45 × the bag price. Comparing those two numbers for the same yard shows which is cheaper for your job.
| Bag | Yield | Bags per cubic yard | Bagged cost per yard |
|---|---|---|---|
| 40 lb | 0.30 cu ft | 90 | 90 × bag price |
| 50 lb | 0.375 cu ft | 72 | 72 × bag price |
| 60 lb | 0.45 cu ft | 60 | 60 × bag price |
| 80 lb | 0.60 cu ft | 45 | 45 × bag price |
Concrete pad and patio cost calculator: common slab sizes
A 12 × 12 ft pad 4 inches thick is 1.78 cubic yards; a 20 × 20 ft slab is 4.94. Multiply the cubic yards by your price per yard, or the bags by your bag price:
| Slab (ft) | Cubic yards | 80 lb bags | Approx. weight |
|---|---|---|---|
| 10 × 10 | 1.23 | 56 | 2.3 US tons |
| 10 × 12 | 1.48 | 67 | 2.8 US tons |
| 12 × 12 | 1.78 | 80 | 3.4 US tons |
| 12 × 20 | 2.96 | 134 | 5.6 US tons |
| 20 × 20 | 4.94 | 223 | 9.3 US tons |
| 24 × 24 | 7.11 | 320 | 13.4 US tons |
Weights use a typical unit weight of about 140 lb per cubic foot for packaged concrete mix.[1] See how much a yard of concrete weighs for the details, and cubic feet to cubic yards for other conversions.
How thick should a concrete slab be?
For house floors, the residential code sets a minimum of 3½ inches.[2] The same section calls for a 4 inch base course where the slab is below grade (with an exception for well-drained soils) and a 6 mil vapor retarder with 6 inch laps, with exceptions such as garages and some flatwork.[2] Patios and walks are not covered by that section; the bagged mix used for this page's yields is rated for pours 2 inches thick or more.[1] Check local code for anything structural.
Base under the slabCompacted gravel under a slab is ordered loose and shrinks when compacted. The paver base calculator and gravel calculator size that layer.
Adding a margin
Bag yields are approximate,[1] and an uneven base adds volume, so it is sensible to order a margin. The Add extra option adds 5–15%, and the cost lines update with it.
Common concrete estimating mistakes
The most common mistake is leaving the thickness in inches: a 10 × 10 ft slab 4 inches thick is 10 × 10 × 0.333 = 33.3 cubic feet, not 400.
- Comparing a bag price with a yard price directly. A cubic yard is 45 bags of 80 lb mix.[1]
- Ordering the exact volume. Bag yields are approximate and an uneven base adds volume, so add a margin.[1]
- Pouring a house floor too thin. Residential floor slabs must be at least 3½ inches.[2]
- Using a pour mix too thin. The standard bagged mix is rated for pours 2 inches thick or more.[1]
- Forgetting delivery and forms. Enter them as fixed costs so both totals include them.
Bags of concrete for a slab
Divide the volume in cubic feet by the bag yield: about 0.60 cu ft for an 80 lb bag, 0.45 for 60 lb and 0.30 for 40 lb.[1] A 10 × 10 ft slab 4 inches thick is 33.3 cu ft, so 56 bags of 80 lb or 75 bags of 60 lb. Round up and keep a bag or two spare. For footings, posts and steps in the same order, use the concrete calculator.
Walls, footings and round columns
Every shape is still volume = area × thickness; only the area changes.
- Wall: length × height × thickness. A 10 ft wall 3 ft high and 8 inches thick is 10 × 3 × 0.667 = 20 cu ft (0.74 yd³).
- Footing: length × width × depth. 20 ft of 16 inch wide footing 8 inches deep is 20 × 1.333 × 0.667 = 17.8 cu ft.
- Round column or post hole: 3.1416 × diameter² ÷ 4 × height. A 12 inch tube 4 ft tall holds 3.14 cu ft, about 6 bags of 80 lb.
Use the circle shape in the calculator for round pours, entering the height as the thickness. Fence post holes, with gravel and the post subtracted, are handled by the fence calculator.
Frequently asked questions
How much does a yard of concrete cost?
Your supplier's price per cubic yard plus any delivery or short-load fee. Bagged, a yard is 45 bags of 80 lb mix, so it costs 45 × the bag price.[1]
How much does a concrete patio cost?
Multiply the cubic yards by your ready-mix price, or the bag count by your bag price, then add delivery. A 12 × 16 ft patio 4 inches thick is 64 cu ft (2.37 cubic yards), or 107 bags of 80 lb.
How much does a 10 × 10 concrete slab cost?
At 4 inches thick it is 1.23 cubic yards. Multiply that by your price per yard and add delivery, or price 56 bags of 80 lb mix.
How many bags of concrete for a 10 × 10 slab?
About 56 bags of 80 lb mix at 4 inches thick, since each bag yields 0.60 cubic feet.[1]
How thick should a concrete slab be?
House floor slabs must be at least 3½ inches thick under the residential code.[2] Patio and walkway thickness is set by the design and local rules.
Is ready-mix or bagged concrete cheaper?
Compare 45 × your bag price against your ready-mix price per yard plus delivery. Enter both in the calculator to see the two totals side by side.