About this site
calctool.cc is a personal project for calculating and interpreting ten dimensionless numbers used in fluid mechanics and heat and mass transfer. It is not run by a company or institution; one person writes and maintains the formulas and guides. No account or sign-in is needed, and calculations run in your browser.
Why it exists
The formulas are scattered across textbooks and lecture notes, and the same symbol can mean different things depending on how the characteristic length and properties are chosen. This site keeps the formula, the input units and the conditions for reading the result in one place. The calculators only evaluate ratios from your inputs; they do not predict material properties or heat-transfer coefficients.
What is here
- Home: the ten calculators grouped into fluid flow, heat transfer, mass transfer, interfaces, and gases and compressibility.
- Calculator pages: for each number, the formula, variables and SI units, unit-conversion pitfalls and how to read the result. For example, the Reynolds number calculator.
- Guides: a basic guide for each number and six calculation notes that chain several calculators together.
- Korean and English pages are separate; the button at the top right of each page switches language.
How the formulas are checked
The formulas live in the public repository non-dimensional-number-calculator. Its tests/check_calculations.cjs loads the same formula file the calculators use and compares worked-example results with hand calculations: for instance that one input set gives Re = 2000, Pr = 7 and Pe = 14000, that Pe equals Re × Pr, and that rounded values published in the calculation notes appear unchanged on both the Korean and English pages. tests/check_site.py checks links, page settings and the sitemap. Both are rerun whenever a formula changes.
How example values and sources are chosen
Examples in the guides, calculators and calculation notes use two kinds of values. The first is a property value with a source. For example, the density of water at 20 °C, 998.2 kg/m³, and its viscosity, 1.0000×10⁻³ Pa·s, come from the saturated-water table in the IAEA’s 2008 compilation of thermophysical properties for nuclear engineering, and the speed of sound in air at 20 °C, 343 m/s, comes from the OpenStax University Physics textbook. Such values are quoted with the temperature and pressure stated in that table. The second is an operating condition that the example explicitly labels as an assumption: pipe diameter, mean velocity or oscillation frequency, for instance.
Sources are preferably public documents anyone can open (NASA, NIST, the IAEA, U.S. Department of Energy laboratories) and university open courseware such as MIT OpenCourseWare. Before a link goes on a page, the document is opened to confirm that the quoted formula or value is actually there, and nothing is attributed to a document that does not support it. The References section at the end of each page names the organisation, the document title and what was checked in it. Examples still exist to show the calculation steps: for design, experiments or safety decisions, recalculate with original data for your actual conditions.
What the checks guarantee and what they do not
The automated checks protect the translation of formulas into code and the numbers printed on the pages. If a guide states “Re ≈ 29,946”, the test script recomputes the value from the same inputs, confirms the rounding, and confirms that the same figure appears on both the Korean and English pages. Changing a formula or an example makes the check fail, so a wrong number cannot stay unnoticed.
Some things the checks cannot verify. They cannot tell whether a quoted property value matches your actual temperature and pressure, or whether a heat-transfer correlation suits your geometry and boundary conditions. Regime labels shown with results, such as “laminar” or “transitional”, are guidance based on boundary values for representative cases like a circular pipe. The Reynolds calculator, for example, labels exactly 4000 as transitional; that is how the code treats the boundary value, not a claim that real flow changes at that number.
Update history
- 2026-01-11: First release of the calculators, with Korean/English switching and a privacy policy and terms (English).
- 2026-01-17: Added visit statistics (Google Analytics 4), usability analytics (Microsoft Clarity) and favicons.
- 2026-09-26: Added a basic guide for each of the ten calculators in Korean and English, and moved guides to extension-free URLs.
- 2026-10-09: Added notes on pipe-flow cross-checks and scale-model comparison, plus theory notes on pressure loss, heat and mass diffusion, gas-flow models and surface-tension time scales, in both languages.
- 2026-10-22: Gave each calculator its own page and grouped the home page by field. Added guide listings, about and contact pages and a 404 page, and rewrote the privacy policy and terms (now also in Korean).
- 2026-10-22: Added real-world examples built from sourced property values, topic-specific FAQs and reference lists to the basic guides, calculators and calculation notes. Added retention periods by service, international transfer details and remedies to the privacy policy.
The full change log is the repository’s commit history.
Found a mistake?
Report calculation or text errors and broken links through GitHub Issues as described on the contact page. When an error is confirmed, the page and the test script are fixed together and the change is recorded in the commit history. If a number was wrong, the corrected value is added to the test script so that the same error cannot return.