Concrete slab calculator
Enter the slab size. Results update as you type.
- Slab area
- 400 sq ft
- Concrete to order
- 5.43 cu yd
- 4.94 cu yd net, plus 10%
- Installed, HomeBlue Austin rate
- $2,400 to $4,000
- Installed, projectcosted Austin rate
- $2,252 to $4,504
- Ready-mix only (no labor, base, steel or delivery)
- $619 to $733
Installed ranges multiply the area by HomeBlue's Austin reinforced-slab rate ($6 to $10 per sq ft, September 2024) and projectcosted's Austin rate ($5.63 to $11.26 per sq ft, August 2026). Ready-mix uses HomeBlue's Austin $114 to $135 per cubic yard. A planning range, not a quote.
The calculator runs in your browser and saves nothing. For an L-shaped or odd slab, split it into rectangles, run each one and add them up.
How the concrete slab calculator works
Volume first, then price. Concrete is sold by the cubic yard, which is 27 cubic feet, so the math is:
Installed price
The installed ranges multiply the slab area by each Austin source's per-square-foot rate. They include labor, forming, base and steel as those sources define them. projectcosted's Austin breakdown puts labor at about half of a typical job and materials at about a third.
Concrete needed for common slab sizes
Here are the sizes people ask about most, worked out at 4 and 6 inches. These are net volumes; add your waste allowance on top.
| Slab size | Area | 4 in thick | 6 in thick |
|---|---|---|---|
| 10x10 | 100 sq ft | 1.23 cu yd | 1.85 cu yd |
| 12x12 | 144 sq ft | 1.78 cu yd | 2.67 cu yd |
| 12x20 | 240 sq ft | 2.96 cu yd | 4.44 cu yd |
| 20x20 | 400 sq ft | 4.94 cu yd | 7.41 cu yd |
| 24x24 | 576 sq ft | 7.11 cu yd | 10.67 cu yd |
| 30x40 | 1,200 sq ft | 14.81 cu yd | 22.22 cu yd |
| 40x60 | 2,400 sq ft | 29.63 cu yd | 44.44 cu yd |
Swipe the table sideways to see every column →
Computed: area x thickness / 12 / 27. Thickened edges, beams and footings add volume a flat-slab formula doesn't count.
Picking the thickness to enter
Thickness changes both yards and cost. The residential code's floor-slab minimum is 3.5 inches; HomeBlue's Austin guide puts residential slabs at 4 to 6 inches; Bullfrog Spas asks for at least 4 inches under a hot tub and 6 or more under a swim spa; steel building supplier MBMI gives 4 to 6 inches for most shop slabs and 6 to 8 with heavy equipment. The slab thickness and rebar guide goes use by use.
What a calculator can't tell you
A flat-slab calculator misses the parts of an Austin job that cost the most to get wrong: thickened edges and beams on clay, rock that has to be broken on the west side, removal of an old slab ($1.10 to $1.70 per square foot on HomeBlue's Austin page), and the pump or extra labor when a truck can't reach the spot. Use the result as a budget check, then compare it with a written quote. The cost to pour a concrete slab in Austin page lists those line items.