LayoutMath is a set of free calculators for the jobs where a wrong number costs real money: decks, stairs, roofs, roof area, rafters, pavers, drainage, squaring a layout and railings. It is an independent project, with no account, no ad network and no paywall.
How the numbers are made
Every formula is printed on its page. The worked examples on each page are computed by the same code as the calculator, so the prose cannot drift from the result. The calculation code is covered by automated tests, including examples where the right answer is known by hand and cases where a simpler formula gets it wrong: the extra rise under a rafter tail, the gaps against a post, a joist span that looks fine by rule of thumb and fails the code table.
Codes and standards
Where a calculator checks against a code, the page names the section. Section numbers refer to IRC 2021 section numbers; England Approved Document K. Local jurisdictions adopt different editions and add amendments, so confirm with your building authority before you buy or cut.
The primary sources behind the pages: the International Residential Code 2021 on ICC Digital Codes, Approved Document K on GOV.UK and the American Wood Council's DCA 6 deck construction guide.
What this is not
These are planning estimates. They do not replace drawings, an engineer, or the code enforced where you build. Beam sizes, footing design, guard loads and drainage design are outside what a calculator like this should decide.
Units
Enter feet and inches, fractions, millimetres or metres. The units default to your browser's region and you can switch them in the header. The choice is remembered on your device only.
Corrections
If a result looks wrong, email hello@layoutmath.com with the page you were on and the numbers you entered. A wrong answer someone can reproduce is the most useful report there is.