A 30x40 slab is 1,200 square feet, and this is shop and barn country. It is a standard pole building footprint, and the slab under it is a different kind of job than a patio ten times smaller in every way except the arithmetic.
The arithmetic part
| Finish | Example rate | 30x40 (1,200 sq ft) |
|---|---|---|
| Standard broom | $9 / sq ft | $10,800 |
| Colored | $12 / sq ft | $14,400 |
Those are example rates to make the math visible, not market prices. Shop slabs get broom finish essentially always; the second row mostly shows how far a finish rate moves a number with four digits of square footage behind it.
The part that separates shop slabs from patios
Volume first. Square feet times thickness in feet divided by 27: about 15 yards at 4 inches, about 22 yards at 6. A shop floor holding equipment, a lift, or loaded trailers wants the thicker pour with rebar, so plan on the bigger number. That is several truckloads, and the trucks have to land in sequence, because concrete on the ground does not wait for concrete on the highway. Run the ordering math with how to figure concrete yardage before you commit a price.
Joints are the other tell. A monolithic 30x40 will crack; the only question is whether it cracks on your lines or its own. The control joint layout gets drawn before pour day.
Reinforcement at the example $1.50 per square foot is $1,800 across this slab. Site prep at the example $2 is $2,400, and on a building pad the grading tolerance is tighter than for a backyard pour, because the walls that come later do not bend.
Price it like the size it is
A slab this size deserves a built rate, not a borrowed one. How to price a concrete slab walks through assembling the rate from mix, labor, and overhead, and the concrete slab cost calculator reruns the example math for any footprint.
When a barn slab inquiry lands, PriceDesk runs this quote with your rates and your add-ons in about ten seconds. Try it free for 14 days.