Slab concrete math is simple when the dimensions stay in the right units: length and width in feet, thickness in inches, then a clean conversion into cubic yards. Construction Pro's Concrete Takeoff also shows bag counts and applies your chosen waste factor in the same result block.
This screenshot comes from the small patio slab pour recording used for this support page.
Concrete orders get expensive when someone mixes feet and inches or forgets the waste factor. These checks help on patios, garage slabs, equipment pads, and any small or mid-size pour where the difference between base volume and order volume matters.
These examples follow the slab preset and the current default bag-yield assumptions in Construction Pro.
Example 1
Inputs: 10 ft x 10 ft x 4 in.
A 4-inch slab is one-third of a foot thick, so the base cubic footage is easy to undercount if you stay in inches too long. Construction Pro calculates about 1.23 cu yd. At the default 80 lb yield, that is about 56 bags when no waste factor is added.
Example 2
Inputs: 24 ft x 24 ft x 4 in with 5% waste.
The base volume works out to about 7.11 cu yd. Once the app applies 5% waste, the ordering number becomes about 7.47 cu yd. That gap is exactly why a visible with-waste line is worth having on the estimate screen.
Example 3
Inputs: 12 ft x 16 ft x 5 in with 8% waste.
A slightly thicker pad pushes the base volume to about 2.96 cu yd. With 8% waste, the result becomes about 3.20 cu yd. That is the more useful number for ordering because it leaves room for jobsite loss and finishing realities.
Common mistakes
Related guides
Because that is how slab thickness is typically called out in the field, and it reduces conversion mistakes during entry.
No. Construction Pro uses bag-yield settings, so the counts follow the current 80 lb and 60 lb yield values in Settings.
The app has a separate footing preset, but the core rectangular-prism math is similar.
Construction Pro keeps slab dimensions, waste, and mix-bag estimates together so you can move faster on site.