By accessing or using this site, you agree to these Terms of Use. If you do not agree, please don't use the site.
Rules of Thumb is a collection of free, browser-based reference calculators organised into
discipline-specific areas — currently Environmental, Mechanical, Electrical,
Finance, Control Systems, Computers, Physics, DIY,
Mathematics, and Health, with more tools added over time. (An older combined
Engineering area was split into Mechanical and Electrical; old /engineering/…
URLs redirect to the new homes.) Every calculator requires no installation, account, or sign-up, and all
calculations run locally in your browser — see our Privacy Policy
for details. New areas and tools may be added to the site from time to time; this policy and
these terms apply to all of them unless a specific tool says otherwise.
Read this carefully. The calculations, charts, and reference data on this site are provided for general informational, educational, and preliminary-estimation purposes only. They are not a substitute for certified engineering calculations, calibrated instrumentation, equipment manufacturer data, or the advice of a qualified, licensed engineer.
Finance tools — please read. Tools in the Finance area do not constitute financial, investment, tax, mortgage, or legal advice, and are not a substitute for a bank, lender, licensed financial adviser, mortgage broker, or accountant. Nothing on this site is a personal recommendation: no tool here knows your circumstances, income, liabilities, tax position, or objectives, and none of them takes those into account.
Rules of Thumb is not authorised or regulated by the Financial Conduct Authority or by any equivalent regulator in any other jurisdiction, and does not carry out regulated activities. Nothing on this site is a financial promotion, an inducement or invitation to engage in investment activity, or an offer to lend, arrange, or advise. Using a calculator here creates no client, advisory, fiduciary, or professional relationship of any kind.
Figures such as interest rates, deposit percentages, historical returns, property taxes, stamp duty and other transaction taxes, insurance costs, and lender criteria are illustrative estimates and typical market values at the time of writing — not quotes, offers, forecasts, or current market data. They change frequently, may already be out of date, and vary by lender, product, credit profile and jurisdiction. Your actual terms from any real institution will differ.
Where a tool models borrowing secured on property, remember that your home may be repossessed if you do not keep up repayments on your mortgage. Property, investment and rental returns can fall as well as rise, past performance is not a guide to future performance, and you may get back less than you put in — or lose money outright. Most buy-to-let lending is not regulated by the Financial Conduct Authority, which means the consumer protections attached to regulated residential mortgages may not apply to it.
Before acting on any figure produced here, obtain advice from a qualified professional who is authorised to give it in your jurisdiction and who can consider your own circumstances.
Tools in the Health area are general educational estimators (for example BMI or energy expenditure). They are not medical advice and must not be used to diagnose, treat, or manage any condition.
Tools in the Control Systems area, and any other simulations on this site, model idealised systems and omit many real-world effects (nonlinearity, time delay, noise, saturation, and more). They are intended to build intuition and must not be used to design, tune, or validate a real control system, mechanism, or safety function without proper analysis of the actual system.
These tools must not be relied upon for safety-critical decisions, life-safety systems, custody-transfer measurement, regulatory compliance, or binding financial commitments. Climate, altitude and location reference data are indicative averages, not measured or forecast values for any specific date.
The site, and all information on it, is provided “as is” and “as available”, without warranties of any kind, whether express or implied, including but not limited to warranties of accuracy, merchantability, fitness for a particular purpose, or non-infringement. You are solely responsible for independently verifying any result before relying on it.
To the maximum extent permitted by law, we exclude all liability for any direct, indirect, incidental, special, or consequential loss or damage — including loss of profit, data, or business — arising from your use of, or inability to use, this site, even if we have been advised of the possibility of such loss.
Nothing in these terms excludes or limits liability that cannot lawfully be excluded or limited, including liability for death or personal injury caused by negligence, or for fraud, under the laws of England and Wales (including the Consumer Rights Act 2015 where it applies) or any other law that applies to you and cannot be contractually excluded.
The design, branding, original written content, and underlying code of this site are © 2026 Rules of Thumb (rulesofthumb.info), unless otherwise stated. The physical formulae and engineering principles used are general scientific knowledge and are not owned by anyone. You're welcome to use the tools for personal or professional reference; please don't copy, scrape at scale, redistribute, or re-host the site's code or design without permission.
You agree not to:
This site is hosted using Cloudflare Pages. Typefaces are self-hosted on this origin
(see the Privacy Policy §6) — your browser does not load Google Fonts.
The Unit Converter’s currency mode may request rates from Frankfurter
(api.frankfurter.dev) when you use that feature. Your use of the site is also subject to
the relevant terms of those providers where applicable.
The site is provided on a best-effort, “as available” basis. We don't guarantee uninterrupted access, accuracy, or error-free operation, and we may modify, suspend, or discontinue the site, or any part of it, at any time without notice.
These terms are governed by the laws of England and Wales, and the courts of England and Wales have non-exclusive jurisdiction over any dispute arising from them. If you are a consumer resident elsewhere — including in the EU/EEA or another country — any mandatory consumer-protection laws of your country of residence will still apply to you and are not overridden by this clause.
If any provision of these terms is found unenforceable, the remaining provisions continue in full effect.
We may update these terms from time to time. We'll update the “last updated” date above when we do.
Use the contact form for corrections to sources or figures, accessibility problems, and privacy requests. There is no public email address; what the form stores is set out in §2b of the Privacy Policy.