How our numbers are calculated

1. The calculation model

Each measurement family has one base unit (metre, kilogram, litre, square metre, kelvin, metre per second, byte). Every unit in that family stores a single factor relative to that base. A conversion is therefore always two steps: convert the input to the base, then convert the base to the target. That avoids the compounding error you get from chained pairwise tables.

Temperature is the exception: it uses affine formulas (°F = °C × 9/5 + 32, K = °C + 273.15) because the scales have different zero points.

2. Where the factors come from

• NIST Handbook 44, Appendix C — US customary and avoirdupois definitions (yard, pound, gallon, acre).
• BIPM SI Brochure, 9th edition — SI base units and their defining constants.
• NIST Special Publication 811 — conversion factor guidance and correct unit usage.
• IEC 80000-13 — binary prefixes for digital storage (KiB, MiB, GiB).
• US FDA 21 CFR 101.9 — the 240 mL cup used on nutrition labels.
• WHO, CDC and NICE — reference ranges used by the health calculators. These are reference ranges, not medical advice.

Every exact value we use is published with its source on the measurement standards pages.

3. Rounding policy

• All arithmetic runs in IEEE-754 double precision; rounding happens only at display time.
• Results of 1000 or more are shown to 2 decimal places.
• Results between 1 and 1000 are shown to 4 decimal places.
• Results below 1 are shown to 4 significant figures, so small values never collapse to zero.
• Conversion pages also show a precision table so you can read the unrounded value when you need it.

Where a conversion is exact by definition (pounds to kilograms, inches to millimetres) we say so. Where it cannot terminate (kilograms to pounds, hectares to acres) we say that too, rather than implying false precision.

4. How the content is written

This site is built and maintained by one small team using an AI-assisted research workflow. Draft explanations are generated with AI, then a human editor checks every numeric claim against the primary sources listed above and re-computes each worked example with the calculator published on the same page.

We state this openly because it is true. We do not publish invented author personas, invented credentials, invented qualifications or star ratings we did not receive. The organisation is the author. See our editorial policy.

5. What we do not do

• We do not give medical, legal, tax or financial advice.
• We do not publish user ratings or review counts, because we do not collect them.
• We do not send your inputs anywhere — the calculators run entirely in your browser.

6. Corrections

If a number here is wrong, tell us via the contact page with the page URL and the source you are citing. Verified corrections are applied within 48 hours and recorded in the changelog below.