Where the values come from
We take bag yields from manufacturer data sheets and, where the maker publishes no volume, from retailer product listings (marked as such). Material weights come from state transportation departments, federal agencies, universities and aggregate producers and, where nothing better exists, landscape suppliers (marked as secondary sources). Depth recommendations from university extension services and industry associations. When sources disagree, we show the range instead of a single number. Where no published figure exists, such as how much topsoil settles, we give our own estimate and label it.
How formulas are tested
The shared calculation code (areas, volumes, bag and truck counts, rebar grids, wall blocks) has a table of inputs with answers worked out by hand. The site will not build unless the code reproduces every answer. Worked examples on each page are calculated from the same data files as the calculator; they are reviewed by hand, not by that automatic check.
Rounding
We keep full precision through the calculation and round only what you see. Anything you buy by the piece, such as bags or truckloads, is rounded up.
Last checked
Values were last checked on 2026-09-26. Each calculator lists its own sources with the date they were checked.