A 20x40 slab is 800 square feet, and this shape usually means one thing: an RV garage bay or a long shop. The vehicle that parks here outweighs anything a normal garage slab sees, which changes almost every decision on the pour.
RV weight is the whole story
An RV or a loaded toy hauler puts serious weight on a handful of axle points, day after day, in the same parking spot. That pushes this slab to the thick end of residential work, with rebar doing the reinforcing instead of light mesh. At the example add-on rate of $1.50 per square foot, reinforcement across 800 square feet is $1,200, and on this slab it is the least negotiable line on the page. The thickness reasoning is laid out in 4 inch vs 6 inch slab.
Volume, in plain arithmetic
Yardage is square feet times thickness in feet, divided by 27. At 4 inches this slab is about 10 yards; at 6 inches it is just under 15. That is more than one truck in most cases, which means timing deliveries so the first pour does not set up while you wait on the second. How to figure concrete yardage has the full method, waste factor included.
The 40 foot length also works the crew. Screed passes run the 20 foot dimension over and over, and the far end of the pour is racing the near end all morning.
Example rate math
| Finish | Example rate | 20x40 (800 sq ft) |
|---|---|---|
| Standard broom | $9 / sq ft | $7,200 |
| Exposed aggregate | $13 / sq ft | $10,400 |
Example rates, not market data. RV bays get broom finish; the aggregate row shows what the same 800 square feet runs as a decorative surface at the example rate.
Site work scales the same way: tear-out at the example $4 per square foot would add $3,200, and grading at $2 adds $1,600. On a pad this long, grade matters twice, because water has 40 feet to find a low spot.
Any other size, same math
The concrete slab cost calculator takes any footprint and runs it against the example rates in seconds.
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