Free · Formulas public · Sources cited
Calculators that show their work.
Free tools for home improvement projects. Every formula public, every source cited, every number checkable against a published standard.
Where to start · by what you're building
Tell us the project, not the tool.
Building a deck
Redoing a room
Concrete + masonry
Heating, cooling + power
Shows the formula
Every input, every intermediate step, every rounding rule is on the page. If the answer looks off, you can trace it.
Cites the source
Rates and code minimums come from manufacturer data, the IRC / IPC / NEC, and industry references, all linked.
Rounds to buyable
You can't buy 2.38 gallons. Results round up to real purchase units, with the raw number shown beside them.
Or start typing your project45 TOOLS · 8 CATEGORIES
Before you buy · decisions that need real math
Buying guides
All guides →Vinyl vs fiber cement siding
30-year total-cost math, fire ratings, and the repaint cycle nobody talks about.
Composite vs PT vs cedar decking
20-year cost breakdown: pressure-treated turns out to be the most expensive option.
Heat pump vs furnace + AC
Climate-zone-by-zone operating costs, with the federal tax credit math worked through.
Every formula visible. Every figure traced to a published standard. Each calculator shows the arithmetic it ran, names the code section or trade standard behind each constant, and links the source so you can check it yourself. Recommendations follow what the numbers say. And if we can't show you how we got a number, we don't publish the calculator: transparency isn't a feature, it's the whole point.