Reference tables
The figures behind every calculator on this site, published in full with the reasoning for each one. If a calculator gives you a number you were not expecting, the explanation is on one of these pages.
Waste factor table
How much extra to order, by laying pattern, room shape and room size. Covers tile, plank flooring, board, concrete and trim, with three worked examples.
Paint coverage rates
Practical coverage per litre by surface, first-coat absorption factors, how many coats each situation really needs, and why the tin's figure is a ceiling.
Adhesive and grout coverage
Consumption per trowel notch, the geometry that derives grout quantity from any tile size, and a live table you can set to your own tile thickness.
How these figures are put together
Each number falls into one of three categories, and we label which:
- Derived. Calculated from geometry, like grout quantity or the number of screws a sheet needs at a given stud spacing. These are the most reliable, because you can check the arithmetic yourself — the formulas are printed on the page.
- Published. Manufacturer or standards figures, like adhesive consumption per trowel notch or bag yields for concrete mix. These vary between brands, usually by 10–20%, so we use a mid-range figure and say so.
- Working estimates. Waste factors and practical paint coverage. These come from merchant estimating practice and installer guidance rather than a single authority. They are deliberately rounded up, because under-ordering costs far more than over-ordering.
Corrections
If one of these figures does not match your experience on site, or your supplier's data sheet contradicts it, tell us. Reference data is only worth publishing if it gets corrected, and a trade figure from someone who fits this material every week is more useful than another chart. We name the change and the date on the page when we make one.
Index last reviewed 2026-09-18.