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 come from university extension services and industry associations. For floors, walls and roofs we use the makers’ own coverage figures and installation instructions (tile setting materials, grout, carpet cushion, wallpaper, shingles and underlayment), industry standards such as CRI 105 for carpet, the tile-setting standard ANSI A108 as quoted by the Ceramic Tile Education Foundation, the Tile Council’s recommendations as cited by Custom Building Products, and the International Residential Code for roof slopes and underlayment. 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, tile and grout, carpet roll layouts, wallpaper strips, roof geometry and roofing materials) has a table of inputs with answers worked out by hand, many of them taken from the makers’ own worked examples and coverage charts. 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, boxes, rolls, bundles or truckloads, is rounded up. Lengths for cutting, such as rafters, are shown to the nearest 1/16 in.
Last checked
Values for the concrete, gravel, soil and landscaping calculators were last checked on 2026-09-26, and those for floors, walls and roofs on 2026-10-05. Each calculator lists its own sources with the date they were checked.