A poured concrete slab typically costs $6 to $12 per square foot installed in 2026, so a 20 by 20 foot garage pad usually lands between about $3,500 and $6,500 once rebar, a gravel base and a permit are included. Doing it yourself can cut that by half or more on small slabs, but the material bill is only part of the job.
Enter your dimensions below to see exactly how many cubic yards or bags you need and what the project should cost, hired out or DIY.
Concrete Slab Cost Calculator
Work out how much concrete you need and what a slab costs, hired out or done yourself.
| Item | Typical | Range |
|---|
Volume = length x width x thickness, converted to cubic yards (27 cubic feet each), plus your waste allowance. Contractor prices are 2026 installed ranges covering forming, placing, finishing and control joints. Many plants charge a short-load fee on orders under about 6 to 10 yards.
How much concrete does a slab need?
One cubic yard of concrete covers about 81 square feet at 4 inches thick, 65 square feet at 5 inches, 54 square feet at 6 inches and about 40 square feet at 8 inches. Always order 5% to 10% extra. Running short mid-pour leaves a cold joint, a weak seam where fresh concrete meets concrete that has already started to set.
| Slab | Thickness | Concrete (with 10% extra) |
|---|---|---|
| 10 x 10 patio | 4 in | About 1.4 cu yd |
| 12 x 16 shed base | 4 in | About 2.6 cu yd |
| 20 x 20 garage | 6 in | About 8.1 cu yd |
| 24 x 36 garage | 6 in | About 17.6 cu yd |
Bags or a truck?
An 80 lb bag of concrete mix makes about 0.6 cubic feet, so one cubic yard takes roughly 45 bags and hours of mixing. Bags make sense for small pads under about one yard, like an AC pad or a few fence posts. Above that, ready-mix delivery is cheaper per yard and far less work, even after a short-load fee. Plan the pour for a mild, dry day and line up help: concrete gives you only a couple of hours of working time.
Frequently asked questions
How thick should a concrete slab be?
Patios, walkways and shed bases are usually 4 inches thick. Garage floors and driveways are typically 5 to 6 inches, especially for trucks. Heavy equipment pads and RV parking may call for 6 to 8 inches with rebar.
Do I need rebar in a concrete slab?
For garages, driveways and foundations, reinforcement is standard and often required by code. For a small patio, welded wire mesh or fiber mesh is usually enough. Reinforcement does not stop cracking, but it holds cracks tight.
How long before I can use a new slab?
You can usually walk on a slab after 24 to 48 hours and drive a car on it after about 7 days. Concrete reaches its design strength at about 28 days, so wait that long before heavy loads.
Is a concrete slab cheaper than pavers?
Usually, yes. A plain broom-finished slab costs less per square foot than most paver installations. Stamped concrete can approach paver prices, while pavers are easier to repair one section at a time.
More free calculators
How this calculator works: concrete volume uses standard cubic yard math. Installed prices come from 2026 national concrete contractor pricing, ready-mix delivery rates and retail material prices, adjusted for thickness, reinforcement, finish and regional labor. Local ready-mix prices and site conditions vary. Figures are estimates as of October 2026. See our disclaimer.
