About
Methodology and Sources
The conventions every calculator follows, and the sources behind the numbers it starts with.
Conventions
Your inputs come first. A calculator never substitutes its own figure for one you have entered. Defaults exist so the page shows a meaningful example; each is labelled and sourced in the assumption table.
Every component is a separate line. Waste, trim, pattern match, back-buttering, mixing allowances, prep, removal and rounding appear as their own rows in the breakdown, never folded into a single figure. If a line surprises you, you can see exactly what caused it.
Units are converted, not approximated. Feet and inches convert to metres and millimetres with exact factors (1 ft = 0.3048 m). Square yards are nine square feet exactly. The result of a calculation is the same whichever system you enter it in.
Averages are averages. Where a default is a national or typical average, it is a starting point, not a claim about your situation.
Waste follows the layout. Boxed flooring adds 10% for a straight layout, 15% for a diagonal and 20% for herringbone, adjusted for the room, the grade and the pattern, and every adjustment is a separate line. Carpet and sheet vinyl have no waste percentage: they are laid out in strips of the real roll width, and the offcut is shown.
Tile counts its joint. A tile is counted by its pitch, the tile plus one grout joint in each direction, not by its face, so tile, grout and layout figures agree with each other.
Rounding happens at the end, and always up for things you buy. Intermediate values keep full precision. Boxes, cartons, rolls, bags, sheets and pieces are rounded up to whole units once; the figure before rounding is shown so you can see how much of the last box you will use.
Ranges, not single prices. Cost calculators report a low and a high figure from dated survey ranges, because that is what the surveys support.
Sources for default figures
| Figure | Source | Used in |
|---|---|---|
| Tile installation, joint widths, flatness for tile and large-format tile, offsets, mortar contact | TCNA Handbook for Ceramic, Glass and Stone Tile Installation; ANSI A108.02 and A118 | Tile group, tile guides |
| Grout coverage | Custom Building Products grout coverage card, used to calibrate the joint-volume formula | Grout calculator, grout and thinset reference |
| Thinset coverage by trowel notch | Coverage charts printed on common US polymer-modified thinsets (Custom Building Products, Schluter for membranes) | Thinset calculator, thinset guide |
| Self-leveler coverage | Manufacturers’ coverage charts (Custom LevelQuik RS: 46–48 sq ft per 50 lb bag at 1/8 in) | Self-leveling compound calculator |
| Box and carton coverage | Manufacturers’ product labels and data sheets (Pergo, Mohawk, Shaw, MSI, Bruce and others) | Plank and box calculators; coverage per box reference |
| Wood moisture limits, acclimation, expansion gap for solid wood | National Wood Flooring Association installation guidelines | Wood group, acclimation planner, expansion gap guide |
| Wood movement with moisture | US Forest Products Laboratory, Wood Handbook, dimensional change coefficients | Expansion gap calculator |
| Floating floor gaps and run limits | Laminate, engineered and vinyl plank manufacturers’ installation instructions | Expansion gap and transition calculators |
| Carpet pad density and thickness | Carpet and Rug Institute standards and carpet manufacturers’ warranty requirements | Carpet padding calculator, padding guide |
| Stair riser and tread limits | International Residential Code R311.7 | Stair carpet and stair flooring calculators |
| Floor heating output, circuit protection | Floor heating manufacturers’ data (12 W per sq ft mats; Schluter DITRA-HEAT about 12.7 W per sq ft); National Electrical Code 424.44 | Radiant floor heating calculator |
| Electricity price | US Energy Information Administration, Short-Term Energy Outlook 2026, residential average about 18 cents per kWh | Radiant floor running cost calculator |
| Installer wages | US Bureau of Labor Statistics, Occupational Outlook Handbook, May 2024 median $25.00 an hour for flooring installers and tile and stone setters | Labour, DIY versus pro and cost calculators |
| Installed, labour and removal prices | Published 2025–2026 cost surveys (HomeGuide, Bob Vila and others), as ranges | Cost group |
| Material life expectancies | Manufacturers’ warranties and published life expectancy charts, as ranges | Lifespan, comparison and budget calculators |
| Asbestos in older resilient flooring | US Environmental Protection Agency (pointer only; no procedures) | Removal calculator, removal guide, disclaimer |
Each calculator’s assumption table names the figure it uses and the date it was last checked. When a source publishes new data, the default and the date are updated together.
What the calculators do not model
They do not inspect a floor. Whether a subfloor is flat enough, dry enough or stiff enough for a finish is a matter of measurement on site, against the limits in the flooring’s own instructions, which always take precedence over any default here. They do not size floor structures: the joist calculator counts framing for a span you choose, but spans and loads are questions for the building code’s span tables or an engineer. They do not design electrical circuits; floor heating figures are loads for planning, and the connection is work for a licensed electrician.
Waste allowances, labour rates, crew-day outputs and life expectancies are standard trade estimating figures, not measurements of your room, your installer or your household. Box coverage defaults are typical; the label on the product you buy is the figure to use. Cost ranges are national, adjusted only by a broad regional factor, and do not predict a particular quote.
Testing
Every calculator carries a set of test cases with hand-worked answers in both unit systems. The tests run automatically before each update to the site, and a calculator that fails any of them is not published. When an error is reported and confirmed, a test case for it is added so that it cannot come back.