Sources & Methodology

Every calculator on ToolBrook links to a Sources section listing exactly what it's built on. This page explains where those sources come from and how we decide a tool is ready to publish.

Where the formulas come from

We prioritize sources in roughly this order: published chemistry or physics (the CO2/pH/KH calculator's carbonic acid equilibrium math, for example), university extension services and government agricultural or fisheries guidance (Mississippi State Extension's chill hour definition, USDA soil region data), established organizations specific to a hobby (INJAF and API Fishcare for aquarium cycling, King Arthur Baking for sourdough), and manufacturer or equipment-maker documentation where it's the most specific guidance available (UMAi Dry's dry-curing weight-loss targets). Every tool page names which of these its numbers come from, not just a vague "experts recommend."

When there isn't a single accepted formula

Some of the most useful calculators on this site don't have one universally agreed-upon equation behind them, sourdough starter timing and seed stratification windows are both like this. In those cases we build a reasonable estimate from the best available guidance and say so directly in the tool's own "how this is calculated" section, rather than presenting an estimate with false precision. Where a range exists in the underlying source, the calculator generally shows a range too, not a single misleadingly exact number.

How we decide what to build

Before a calculator gets built, we check who's already solved that exact problem. If a specific tool is already well covered by an established site, an extension resource, or a strong niche competitor, we don't build a copy of it. A few of our own tool pages say this outright and point to the better option (the rain garden sizing calculator credits UConn CLEAR's Rain Garden App for the 23 states it covers, for example). We'd rather build fewer tools that genuinely add something than a large number of pages that just duplicate what already exists.

Keeping tools current

Each tool page shows a "reviewed against" line and a last updated date. When underlying guidance changes, meaning a source organization revises its recommendation, we update the calculator and the date. If you spot a source that's gone stale or a formula that looks wrong, the Contact page has a direct way to flag it.