Slab is the catch-all job: shed bases, additions, mower pads, whatever does not have its own name. That is exactly why it needs a method instead of a gut number. The method is four moves.
Measure, rate, add-ons, minimum
Measure. Length times width. A 20 by 20 shop slab is 400 square feet. Odd shapes break into rectangles; measure each and add them.
Rate. Multiply by your per-square-foot rate for the finish. At the example broom rate of $9, that 400 square foot slab is $3,600. Your real rate comes from your costs, not from a chart on the internet.
Add-ons. Reinforcement, tear-out, and grading go on as separate lines. Rebar or mesh at the example $1.50 per square foot adds $600 to the 400 square foot slab, and the customer sees exactly what it buys.
Minimum. Below a certain size the math stops working, because the truck, the crew, and the forms show up regardless. Set a floor and hold it. How to set a minimum job charge walks through it.
Thickness follows the load
The rate you apply should already assume a thickness, so decide thickness first.
- 4 inches: foot traffic, patios, shed bases, sidewalks.
- 5 to 6 inches: cars and trucks, garage floors, RV pads.
- More than that: heavy equipment territory, which means an engineered spec, not a thicker guess.
Thickness is not a small detail. Going from 4 to 6 inches is half again as much concrete in the same footprint, so a single all-purpose slab rate will quietly lose money on thick pours. The 4 inch vs 6 inch slab comparison shows what the jump does to a quote.
The yardage sanity check
Before any slab number goes out, check it against the concrete order: square footage times thickness in feet, divided by 27. The 400 square foot slab at 4 inches is 400 times 0.33, about 133 cubic feet, which is just under 5 yards. At 6 inches it is 200 cubic feet, about 7.4 yards. If the yardage bill would eat the quote, the quote is wrong. Full walkthrough in how to figure concrete yardage.
Run your own numbers on the concrete slab cost calculator. Then put your real rates into PriceDesk and every slab, shed base, and odd pad quotes itself from your phone in about ten seconds. Free for 14 days.