All Unit Conversions

About AllUnitConversions.com

AllUnitConversions.com is a free technical reference for converting units used in engineering, science, aviation, shipping, and everyday measurement. The site is built around a shared conversion-factor library and interactive calculators. It is not built around named reviewers, awards, or invented credentials.

Mission and who it is for

The mission is to give working technical users a fast, transparent place to convert a value and see the relationship behind the result. The primary audience already knows which quantity they are converting and needs a published factor they can check: mechanical and electrical engineers moving between SI and customary units; students doing dimensional analysis; scientists converting SI derived units; pilots converting fuel, airspeed, and altimeter settings; and freight operators converting TEU capacity, chargeable weight, and bunker volume.

Everyday pairs — length, mass, temperature, kitchen volume — use the same library. The site is not a substitute for a certified calibration laboratory, a licensed engineer’s stamp, an aircraft or vessel operating manual, or legal-for-trade measurement.

What the site covers

Category hubs include length, mass, temperature, volume, speed, pressure, power, energy, force, electricity, magnetism, radiation, heat, fluid, light, sound, and related engineering quantities. Specialty hubs cover aviation, shipping, and a smaller set of engineering calculators (beam deflection, circuit analysis, thermodynamic properties). Companion formula and chart pages publish the same relationships as equations and tables. The calculator index and science hub are the shortest paths into those tools.

Data sources

Conversion factors come from published definitions, not from crowd-sourced spreadsheets. The main references are:

  • BIPM SI Brochure — governing reference for SI base units, derived units, and the 2019 redefinition that fixed the kilogram, ampere, kelvin, and mole to fundamental constants.
  • NIST SP 811 and NIST SI / weights and measures — SI usage and U.S. customary equivalents used on engineering and everyday pages.
  • International Yard and Pound Agreement (1959) — defines the international inch as exactly 25.4 mm, the foot as exactly 0.3048 m, and the avoirdupois pound as exactly 0.45359237 kg. Those exact relations are the basis for most imperial and U.S. customary length and mass conversions here.
  • IEC Electropedia — electrical and magnetic quantity names and relationships.
  • CIE International Lighting Vocabulary — photometric terms used on light-conversion pages.
  • ICRP — radiological-protection quantity definitions used when converting dose and activity units.

Where a factor is an exact convention (1 in = 25.4 mm; 0 °C = 273.15 K), the library stores that definition. Where a quantity is only conventionally related — planning fuel density, typical dry-van internal volume, bunker density defaults — the tool page labels it as a planning figure. Currency and live FX rates are not treated as static SI factors and are handled separately from the conversion library.

How conversion factors are maintained

Multiplicative conversions go through one shared library. Each unit has a factor relative to a coherent base for that quantity, and the calculator computes (value × fromFactor) / toFactor. Temperature is the main exception and is converted through kelvin.

SI and the 1959 customary definitions change rarely. There is no daily recalibration of the meter or the pound — those are defined constants. The library is updated when BIPM, NIST, IEC, or a domain standard body publishes a definition change, when a user reports a wrong factor or a mislabeled unit, or when a new category or specialty tool is added. Affected pages are then redeployed.

We do not claim a published quarterly audit by an external metrology laboratory. Aviation and shipping planning values (for example Jet A at 6.7 lb/US gal, typical container CBM, or default bunker densities) are documented on those tool pages and are not presented as SI constants. Prefer the fuel ticket, CSC plate, or BDN density for operational decisions.

Precision and IEEE 754

Calculations run as IEEE 754 binary64 floating-point numbers — the JavaScript Number type — in the browser and on the server. Binary64 has a 53-bit significand, which is about 15–17 decimal digits of precision for a single stored value.

That is not the same as “every displayed result has 15 accurate digits.” On-screen answers are usually rounded for readability (commonly about six significant figures, or scientific notation for very large or small magnitudes). Intermediate arithmetic still uses binary64, so some decimal fractions cannot be represented exactly. Exact SI and customary definitions remain exact as ratios; binary floating-point is an approximation of those decimals.

For homework, shop drawings, and most engineering checks, the displayed result is sufficient if you account for that rounding. For safety-critical, legal-for-trade, or calibration work, verify against the primary standard and your organization’s approved procedure. This site does not claim measurement traceability or an accredited uncertainty budget.

What we do not claim

AllUnitConversions.com does not publish fictional staff bios, purchased reviews, or invented academic titles. Where a page mentions an editorial team, that means the site operators who maintain the conversion library and documentation. If a value needs a named subject-matter review that we do not have, the page labels the value (for example, as a planning density) instead of inventing a reviewer.

Contact

Corrections to a factor are more useful than a general comment. Include the page URL, the units and value you entered, the result you expected, and the standard you are citing if you have it. We aim to reply within 24–48 business hours.

These paths are repeated on the contact page. Privacy and usage terms are in the privacy policy and terms of service.