20×30 Concrete Slab Cost
A 20×30 slab covers 600 square feet. Here's the concrete, bags and cost for 2026 — a common size for a garage / large patio.
Concrete (4", waste in)
8.15 yd³
367 × 80 lb bags
Materials (ready-mix)
$1,079 – $1,723
delivered, 4" slab
Installed by a pro
$3,300 – $7,200
4" slab, national average
20×30 slab cost calculator
Adjust thickness, waste or region — the cost updates live.
Waste & region
Order extra for spillage & uneven subgrade. 10% is typical.
Installed cost estimate
$3,300 – $7,200
600 sq ft · 8.15 yd³ concrete
Bags of concrete needed (rounded up)
367
80 lb
489
60 lb
587
50 lb
734
40 lb
- Ready-mix (delivered)
- $1,079 – $1,723
- Bagged mix (80 lb, DIY)
- $2,019 – $3,303
- Installed by a pro
- $3,300 – $7,200
Estimate only — not a quote. Bag counts are rounded up and include a 10% waste allowance.
20×30 slab cost by thickness
| Thickness | Concrete | 80 lb bags | Ready-mix | Installed |
|---|---|---|---|---|
| 4" | 8.15 yd³ | 367 | $1,079 – $1,723 | $3,300 – $7,200 |
| 5" | 10.19 yd³ | 459 | $1,273 – $1,935 | $3,750 – $7,650 |
| 6" | 12.22 yd³ | 550 | $1,528 – $2,322 | $4,200 – $8,100 |
Includes a 10% waste allowance; bag counts rounded up. National US averages, January 2026.
You'll also need
Sized for this exact slab — tap any item to open its calculator with your measurements already filled in.
20×30 concrete slab: what to expect
A 20×30 slab covers 600 square feet. At the standard 4" thickness it takes about 8.15 cubic yards of concrete once you allow 10% for waste, which is roughly 367 × 80 lb bags if you mix by hand. Stepping up to 6" — sensible if it'll carry a vehicle — raises that to about 12.22 cubic yards.
Budget around $3,300 – $7,200 to have a 4" slab this size poured and finished by a contractor, or roughly $1,079 – $1,723 in ready-mix if you're doing the labor yourself. On top of the concrete you'll need about 8.52 yd³ of gravel base and 42 sticks of rebar.
Compare nearby sizes
Planning something bigger or smaller? Jump straight to the cost for a nearby size.
Volumes use standard bag yields and a 10% waste allowance; costs are national US averages that vary by region, mix and finish. See our methodology for exactly how each figure is worked out, or check the reference sources: