How much does a 20x20 concrete slab cost?
A 20x20 slab is 400 square feet. In 2026, a plain 4 inch residential slab commonly lands around $2,600 to $5,200 installed before unusual site prep, reinforcement, or decorative finishes.
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Concrete Slab Cost Calculator
Estimate slab cubic yards, ready-mix cost, finish cost, labor, and total installed price for patios, sheds, garage pads, and flatwork.
Estimate$2,950 - $4,900 installed
- Slab area
- 400 sq ft
- Concrete with 10% waste
- 5.4 cu yd
- Ready-mix material
- $750
- Installed cost per sq ft
- $7.37 - $12.25
Estimating Notes
- Use 4 inches for patios and sidewalks; use 5 to 6 inches for heavier garage or driveway slabs.
- Add 10% waste before ordering concrete, especially if the subgrade is uneven.
- Stamped finishes can cost more than the concrete itself, so compare plain and decorative results before quoting.
Calculator FAQs
How many yards are in a 20x20 slab at 4 inches?
A 20x20 slab at 4 inches is about 4.94 cubic yards before waste and about 5.5 cubic yards after adding a 10% ordering allowance.