20×40 Concrete Slab Cost
A 20×40 slab covers 800 square feet. Here's the concrete, bags and cost for 2026 — a common size for a RV pad.
Concrete (4", waste in)
10.86 yd³
489 × 80 lb bags
Materials (ready-mix)
$1,358 – $2,064
delivered, 4" slab
Installed by a pro
$4,400 – $9,600
4" slab, national average
20×40 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
$4,400 – $9,600
800 sq ft · 10.86 yd³ concrete
Bags of concrete needed (rounded up)
489
80 lb
652
60 lb
783
50 lb
978
40 lb
- Ready-mix (delivered)
- $1,358 – $2,064
- Bagged mix (80 lb, DIY)
- $2,690 – $4,401
- Installed by a pro
- $4,400 – $9,600
Estimate only — not a quote. Bag counts are rounded up and include a 10% waste allowance.
20×40 slab cost by thickness
| Thickness | Concrete | 80 lb bags | Ready-mix | Installed |
|---|---|---|---|---|
| 4" | 10.86 yd³ | 489 | $1,358 – $2,064 | $4,400 – $9,600 |
| 5" | 13.58 yd³ | 612 | $1,698 – $2,580 | $5,000 – $10,200 |
| 6" | 16.3 yd³ | 734 | $2,037 – $3,096 | $5,600 – $10,800 |
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.
20×40 concrete slab: what to expect
A 20×40 slab covers 800 square feet. At the standard 4" thickness it takes about 10.86 cubic yards of concrete once you allow 10% for waste, which is roughly 489 × 80 lb bags if you mix by hand. Stepping up to 6" — sensible if it'll carry a vehicle — raises that to about 16.3 cubic yards.
Budget around $4,400 – $9,600 to have a 4" slab this size poured and finished by a contractor, or roughly $1,358 – $2,064 in ready-mix if you're doing the labor yourself. On top of the concrete you'll need about 11.36 yd³ of gravel base and 55 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: