Guides

The measuring methods, standard dimensions, and material reasoning behind every calculator, in enough depth to answer why a calculator asked you something as well as what the answer was.

A calculator applies a number; a guide explains it. Where a calculator uses ten per cent waste, the guide says why cut geometry produces ten per cent for a straight lay and closer to twenty for herringbone. Where a calculator assumes 350 square feet per gallon, the guide says what that figure assumes about the surface and when it stops being true. That division is deliberate — it keeps the two page types from restating each other, and it means you can read either one without the other.

Four kinds of guide live here. Method guides cover how to measure something specific — a roof from the ground, an irregular yard, a kitchen whose walls are not plumb — with the arithmetic written out rather than described. Reference guides are tables worth coming back to: nominal against actual lumber dimensions, sheet sizes and their real net coverage, brick and block modules, fastener sizes and counts per pound. Trap guides cover the places where a unit changes underneath you, which is where most estimating errors that survive a double-check actually come from. And sourcing guides say where this site's own constants originate, and which of them are published figures rather than conventions.

Guides link down to the calculators that apply their reasoning, and calculators link up to the guide that explains their constants. If you arrived from a calculator wanting to know why a figure is what it is, you are in the right place; if you arrived here first, every guide ends somewhere you can put the reasoning to use.

Each guide is written to stand on its own, and carries worked numbers wherever a formula is easier to follow with real values in it than stated abstractly. Nothing here is a longer version of a calculator page — if a guide could be folded into a calculator's method section without losing anything, it would not have been written.

Some of these are worth bookmarking rather than reading once. The dimension references and the unit-conversion tables stay relevant across every future project, not just the one that sent you looking for them, and they are the pages most likely to settle an argument on site.