The things people ask most about how FastCalc works, where the numbers come from, and what to expect. If your question isn't here, just ask.
Yes — every calculator is completely free to use, with no account, sign-up, or paywall. There's no premium tier hiding the useful features, either.
We trace each formula to an authoritative source and check it against reference values where we can before it goes live. We also try to state the assumptions and limits on each page, so you know what a number does and doesn't account for. Getting the math right is the whole point of the site.
From primary sources only — government agencies, recognised engineering standards, and peer-reviewed work. We list the sources on each calculator so you can follow them and confirm the math yourself, rather than taking our word for it.
No. Calculators run entirely in your browser, and the values you enter never leave your device. There are no tracking pixels and no advertising scripts. See the privacy page for the full details.
Because we add one carefully made tool at a time. Each has to clear the same checklist — verified formula, worked example, common mistakes, and cited sources — before it's published. We'd rather have a small library you can fully trust than a huge one you have to second-guess.
We add new tools regularly, as often as we can while keeping the quality up. Some weeks bring more than one; the pace depends on how long each takes to get right. Real requests help decide what comes next.
Absolutely, and we'd welcome it. Send the details through the contact page — what you're trying to work out and who it's for — and it goes straight onto the list.
Please tell us. We take every report seriously, check it against the original source, and fix confirmed errors as soon as we can. The fastest way is the contact page, with the calculator name and the inputs you used.
Once a page has finished loading, the math runs locally in your browser with no further connection needed. As long as the page is open, you can keep using it offline.
Yes. Every page is built to be fast and fully usable on any device, from a small phone to a large monitor. The calculators are designed for touch as much as for a mouse.
No, the site is currently ad-free. Our goal is a fast, clean experience where the tool is the focus — not the surrounding clutter.
Each tool is built and reviewed by our small team. We're not hiding behind anonymous "experts" — every formula is traced to a primary source and cited openly, so the work can be checked rather than simply believed.
We're happy to explain how a formula works or where a number comes from.
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