A 24x30 slab is 720 square feet: the oversized garage, or the compact three-car. It is what people pour when a 24x24 slab almost fits the plan but the boat, the mower, or the third vehicle says otherwise.
What the jump from 24x24 actually costs
Here is a size-specific observation worth having in your pocket. Going from 24x24 to 24x30 adds 144 square feet, which at the example broom rate of $9 is $1,296 more. But the crew, the mobilization, and most of the forming were already being paid for. The last 144 square feet of a slab is always cheaper to produce than the first 144, which is why quoting the upsize is usually good business for both sides of the driveway.
Example rate table
| Finish | Example rate | 24x30 (720 sq ft) |
|---|---|---|
| Standard broom | $9 / sq ft | $6,480 |
| Colored | $12 / sq ft | $8,640 |
As always on these pages, those are example rates for the math, not market prices. Garage and shop floors at this size take broom finish nearly every time.
Volume and thickness at 720 square feet
Concrete grows fast at this footprint. Square feet times thickness in feet, divided by 27: about 9 yards at 4 inches, about 13.3 yards at 6. If vehicles park here daily, and on a slab this shape they will, the thicker pour with reinforcement is the standard call, and the extra yardage has to be in the price on day one. How to figure concrete yardage walks through the ordering math, waste factor included.
The example add-ons scale up accordingly: tear-out at $4 per square foot is $2,880, site prep at $2 is $1,440, and mesh at $1.50 is $1,080. Any one of those left off the quote comes straight out of margin.
Run any footprint
The concrete slab cost calculator opens preloaded with this size, and reruns for anything else while the customer is still talking.
Swap the example rates for your own in PriceDesk and this whole quote takes about ten seconds from the jobsite. Free for 14 days.