About RenoMath
RenoMath is a small collection of estimating tools for home improvement work. It exists because the arithmetic behind most renovation decisions is simple, but the inputs are scattered across product labels, contractor quotes and rules of thumb that contradict each other.
Every calculator here runs entirely in your browser. The arithmetic never leaves your device, and you can use all of it without an account.
How the numbers are produced
Material calculators use standard coverage rates: 350 sq ft per gallon of interior paint, 32 sq ft per 4x8 sheet of drywall, 0.60 cubic feet per 80 lb bag of concrete mix. Cost estimators use US national averages for labour and materials, updated periodically, and always return a range rather than a single figure.
Where the figures come from
Every calculator lists its assumptions on the page rather than hiding them in a methodology note nobody reads. Material coverage rates — 350 sq ft per gallon of paint, 32 sq ft per drywall sheet, 0.60 cubic feet per 80 lb bag of concrete — are the manufacturer-published figures printed on the packaging, not rules of thumb passed between job sites. Where a product genuinely varies, such as thinset coverage which depends on trowel size, the page says so and returns a range instead of a confident single number.
Cost estimates are built from published regional and national averages for labour and materials. They are coarse by design: the point of a range is that it survives being wrong. A contractor quoting inside the range is plausible; one quoting 40% below it is quoting different work, and that difference is worth a conversation before anything is signed.
How the numbers move
Prices and coverage rates change. We review the cost baselines periodically and when a reader sends us a figure that is clearly out of date. When a formula itself turns out to be wrong, we fix it and note the correction rather than editing quietly, because someone may already have ordered material based on the old answer. If you spot a number that looks wrong for your region or your product, tell us — a specific message with the calculator name and your inputs is far more useful than "this seems off".
Why there is no sign-up wall
A calculator that asks for an email before showing a number is a lead capture form wearing a tool's clothing. Everything on this site works without an account, and the arithmetic runs inside your browser, so nothing you type is transmitted anywhere. That constraint is deliberate: it keeps the site fast, it means the tools work offline once loaded, and it means the numbers are yours rather than something we can mine.
What these tools are not
They are not quotations, engineering advice or a substitute for a site visit. Structural work, electrical, gas and anything involving a permit needs a licensed professional who has seen the building. Use these figures to prepare better questions, not to replace the person answering them.