Editorial Guidelines · Milli to Micro

Which sources we treat as authoritative

We do not derive SI prefix values ourselves and we do not cite other converter websites. Factors come from the primary standards documents, in this order of precedence:

The SI Brochure, 9th edition (BIPM, 2019) — the defining document for the International System of Units, published by the Bureau International des Poids et Mesures. Table 7 defines the SI prefixes. Where anything on this site disagrees with the SI Brochure, the SI Brochure is right and we have a bug.
NIST SP 811, Guide for the Use of the SI — used for style and usage questions the Brochure leaves open: symbol spacing, capitalisation, plural forms, and which prefix conventions are acceptable in technical writing.
ISO/IEC 80000 — consulted for quantity definitions and for the non-SI units that appear alongside SI ones in practice, such as the bar, the rem, and the mil.

Why these conversions are exact

SI prefixes are definitional, not measured. Milli is defined as 10⁻³ and micro as 10⁻⁶ — they are exactly three powers of ten apart, so every milli-to-micro conversion is exactly ×1,000 and every micro-to-milli conversion is exactly ÷1,000. There is no experimental uncertainty, no revision history, and no significant-figure judgement involved.

This is worth stating plainly because it is unusual. Most conversions you will meet — pounds to kilograms, Fahrenheit to Celsius, calories to joules — carry a definitional factor that has been revised at some point, or a rounding convention. SI prefix conversions carry neither.

How the arithmetic is performed

Multiplying by 1,000 in binary floating point does not always give the answer you expect. In IEEE-754 double precision, 1.001 * 1000 evaluates to 1000.9999999999999, not 1001. A converter that multiplies naively will show that, and on a site whose entire claim is exactness, that is not acceptable.

Every conversion on this site instead adjusts the decimal exponent of the number as written and re-parses it. Shifting 1.001 by three powers of ten produces the string 1.001e3, which parses to exactly 1001. This is exact for every decimal value a person can type into the box, which is the only input space that matters here.

What we will not do

We do not round silently. Values are displayed as computed. Where a number is too large or small to show in full it is switched to scientific notation rather than truncated.
We do not invent precision. The converter never adds significant figures your input did not have.
We do not publish conversions we cannot source. If a unit pair is not covered by the standards above, it does not get a page.
We do not treat non-SI lookalikes as SI. The mil, the micron of mercury, the rem, and the gauss all appear in real engineering documents next to SI units and all convert differently. Where a page touches one, it says so.

Review and corrections

Review

Conversion factors are checked against the SI Brochure when a page is created and re-checked whenever the page is materially edited. Because SI prefix definitions are stable, the practical risk is not that a factor becomes outdated — it is that a page contains a typo, an inverted exponent, or a domain claim that is wrong in context. Those are the errors we look for.

Corrections

We correct errors rather than quietly deleting pages. If you find one, email hello@millitomicro.net with the URL and the specific sentence or number involved. Reports that identify an exact location get fixed fastest. Substantive corrections to a published figure are noted on the page rather than made invisibly.

Independence and advertising

Conversion factors are determined by the standards bodies named above and by nothing else. No advertiser, affiliate, or sponsor influences a number, a recommendation, or which unit pairs get a page. Where this site carries advertising, it is labelled as such and served separately from the editorial content.

Use of automation

Conversion tables and worked examples on the converter pages are generated programmatically from the factor definitions — that is deliberate, because generated arithmetic does not make transcription errors the way retyped arithmetic does. Explanatory prose, domain context, and the guidance about when each unit is appropriate are written and reviewed by people. Any page where that distinction matters says which is which.

Limits of this tool. The arithmetic here is exact, but arithmetic is not the whole job. Several quantities on this site — medication strengths in mg and µg, radiation dose in mSv and µSv, infusion rates in mL/min — sit in contexts where an error causes real harm. Nothing on this site is medical, clinical, or safety advice, and a converted number should never be the only check before it is acted on. Verify against the protocol, the datasheet, or the prescriber.