Every calculator and chart here is built the same way. Here's the process, so you can judge whether to trust it.
Sources
I don't invent values. They come from three places. Manufacturer sizing guides and spec sheets, like the generator worksheets Generac and Honda publish, or the coverage tables Mitsubishi and Daikin print for mini-splits. Code references where they apply, like NEC rules for transfer switches. And established load methods like ACCA Manual J, which I simplify for planning use and say so when I do.
The two-source rule
No number ships on the strength of one source. Each value gets checked against at least two independent references. When sources disagree, I use the conservative one and note the range.
What these tools are not
They're planning estimates. Good enough to size a purchase or sanity check a contractor's quote. They are not engineering. Wiring a transfer switch, designing whole home HVAC, anything structural: that's a licensed professional's job, and every page that touches those topics says so.
Updates
Pages show a review date. When a spec changes or a code cycle updates, I fix the page and note it.
Found a wrong number?
Tell me which page and which value, ideally with your nameplate or spec sheet. Contact. Corrections jump the queue.