How we build the calculators and cheat sheets

Who makes them

The site is built and written by Ian MacCallum, founder, diyproject.ai, as the free public side of Blueprint, a home maintenance and project tracker made by Parra.

Formulas are code, and the code is tested

Each calculator's math lives in one shared module rather than inside the page, and most of those modules have automated tests that check known inputs against known answers. A change that breaks a result fails those tests before it can reach the site.

Results are estimates for planning

The calculators run entirely in your browser and nothing you type is sent anywhere. Their results are estimates to plan and shop with, including a waste allowance where the material calls for one. Real rooms are rarely square, and products vary, so buy with a margin.

Local code comes first

Sizing, span, load and wiring figures follow common practice, but your local building code and the product's own instructions govern. For permitted, structural, gas or electrical work, confirm the plan with your inspector, a licensed pro or an engineer before you start.

Found a mistake?

Tell us through the contact page with the page and the numbers you used. Corrections are made in the shared module, so a fix reaches every page that uses that formula at once.