Where the numbers come from
- Building codes: the International Residential Code (IRC), the model code most US states and cities adopt, for limits such as stair riser height or the room around a toilet. See Sources and building codes.
- Accessibility: the 2010 ADA Standards for Accessible Design, for accessible heights and clearances.
- Makers’ specifications: size charts and spec sheets from door, window, cabinet, toilet and mattress makers.
- Industry guides: for example the American Wood Council’s deck guide (DCA 6) and the ENERGY STAR room air conditioner sizing chart.
Numbers link to the page they came from, and each page ends with its full source list. When sources disagree, the page shows the range and says whose figure is whose.
How the drawings are made
The drawings are built from the same numbers as the charts and calculators, at true scale, not traced from photos. When you switch between inches and centimeters, the labels change; the drawing stays to scale.
How the calculators work
Each calculator shows its math, so you can check it. Materials are rounded up to what you can actually buy, such as whole boxes of tile, with a waste allowance shown separately. Lengths are given to the nearest 1/16 in.
Updates and corrections
Each page shows the date it was last updated. Codes and products change, so check the sources before you build. If you find a mistake, send us a message with the page and the number.