The reports of the death of the micron are greatly exaggerated

After a two month break, Metric Views returns with an article by UKMA’s new Chairman, John Frewen-Lord, about an aspect current metric usage. (With apologies to Mark Twain for the headline).

The modern Système Internationale (SI) is supposed to be language-independent i.e. metric measurement unit symbols appear the same no matter the language of the country in which they are used. It is therefore interesting to note that the so-called ‘micron’ – an obsolete unit deprecated in SI – appears to be alive and well, and its death obviously greatly exaggerated.

The micron is of course a ‘slang’ term for the micrometre – symbol µm – and equal to 1/1000th of a millimetre. Yet the term ‘micron’ refuses to die. It keeps cropping up in all sorts of situations – some at the industrial level, and some at the ‘retail’ level. The problem with using the term ‘micron’ (as opposed to micrometre) is that the symbol µm does not seem to be directly related to it, even though the micrometre and the micron are the exact same unit (in fact, the use of the µ by itself is often used to mean the micron). Consequently, whenever the term ‘micron’ is used, it usually has to be spelt out in full – the very antithesis of what SI is about.

Because most metric units (including the micron) very often have different spellings in different languages (which the use of the standard language-independent SI symbols is designed to obviate), it means that whenever it is used in specifications, product descriptions, instruction manuals and the like, it has to be spelt out for each language. Very different spellings can be encountered for the micron in everything from specified coating thicknesses used in industrial processes to ultra-thin sheeting used in the construction industry as well as all sorts of manufactured products.

One product encountered at the retail level, seen in a specialist printer’s supply shop, is a particular brand of A4 laminated sheet pouches (manufactured in Eastern Europe). While the length and width are specified using the correct mm symbol, the thickness is spelt out using the term ‘micron’ – in fourteen Western and Eastern European languages! Thus the packaging shows the pouch size as 303 mm x 216 mm (to fit an A4 sheet), with the thickness shown as follows:

English – 75 Micron

French – 75 micron

German – 75 Mikron

Spanish – 75 micrón

Italian – 75 micron

Portuguese – 75 mícron

Swedish – 75 mikron

Norwegian – 75 Mikrometer (the correct term for a µm)

Finnish – 75 mikroni

Polish – 75 mikronów

Czech – 75 mikron

Hungarian – 75 mikron

Slovakian – 75 mikrónov

Turkish – 75 mikron

It seems such a waste of space on the packaging for all these different versions of the word ‘micron’ to be printed out, not to mention the time it must have taken someone to look up all the translations. Why can’t the proper term ‘micrometre’ and its symbol µm be used in all cases?

The pouch size then could be simply shown – just the once – as 303 mm x 216 mm x 75 µm. Metric units used as they should be.

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6 Responses to The reports of the death of the micron are greatly exaggerated

  1. BrianAC says:

    Whilst I am in total agreement with this, I use the word 'micron' verbally but would not write it as such, using µm in the written form. The main problem is probably the fact that there is no single computer keystroke for these symbols, like the squared superscript (²) is often just a 2, very few people have the character map on their desktop as I do. Some simple text editors (and advanced programmes) may not reproduce these correctly. Having just tested this, 'notepad' does work correctly.
    However, this in no way excuses professional printing and speech. The above example can only be put down to stupidity.
    On a similar tone and more in the public domain, I find it really irksome that in Formula one motor racing they use the terms like 'three-and-a-half one hundredths of a second' when 35 ms would seem much easier to understand as the timing is always to the nearest ms (even easier if it is seen as 0.035 seconds on the readout). Having said that, they do give speeds mostly in km/h now, so that is one bit I understand!

  2. John Drinkwater says:

    Let’s fix the keymaps then, Brian.

    I’m on Linux with a British key layout, and µ can simply be brought up with the key press alt gr+m.

  3. Ed the yank says:

    Hi Brian and John D.,
    In the US in the medical field, vitamin bottles and some trade journals, mcm for µm and mcg for µg are used.

  4. BrianAC says:

    Linux or Windows, PC or Mac, the Greek symbols are not part of the ASCII keyset. Hot keys can be programmed to do anything you want. I guess by using a Greek keyboard the Greek symbols would be there, but other computers would print the things differently, it is down to the page code file. Western Europe can use page 850 or the older page 437, I remember well the days of writing that line into the 'autoexec.bat' file. Here is a Wikipedia link
    Anyway, the 'micron is a lot better than the 'Ångstrom' that preceded it.
    The real problem is in the general reluctance to use the proper symbols in the first place.
    I notice also on UK TV the frequent use now of 'millions of meters' instead of 'thousands of km'. That makes New York 5,500,000 meters from London rather than a more user friendly 5,500 km, there is a definate reluctance to use the km for anything, it has to change to 'miles', almost as if the media think the illigal use of the km on UK roads extends to its use elsewhere in UK. Back to THAT one again. Of course its ok for cameras to have 'MegaPixels' and laptops to have 'Gigabits' but heaven forbid we should dare use them for general reference.

  5. John Steele says:


    Codepage 437 doesn't support many languages. Codepage 1252 is Windows-Western Latin-1 and supports most Western European languages. Opening character map and dragging symbols to your document is a bit clumsy. For Windows users with a numberic keyboard, using "alt codes" is easier. Hold down the alt key while typing a 1-3 digit number for codepage 437 references, or four digit (requires leading zero) to whatever modern codepage is in use. If codepage 1252, the alt code for the micro symbol is 0181.

    I'm not sure if html special characters are permitted (or interpreted) here. They lead with an ampersand and close with a semicolon, surrounding an entity reference. The entity may be an assigned name, decimal number, or hex number. For the micro symbol, named reference is micro, decimal is #181, hex is #xB5. Attempting to render 75 micrometers each way:
    75 µm (alt key)
    75 µm (named reference)
    75 µm (decimal reference)
    75 µm (hex reference)

    The named reference is quasi-readable to humans if the browser doesn't represent it correctly.

  6. John Steele says:

    Getting back to the original problem of continued use of the term "micron," it was originally sanctioned by the BIPM and governing committees, but is now obsolete.

    In reviewing decisions in the back of the SI Brochure:
    *The unit name micron and symbol µ are listed in Resolution 7 of the 9th CPGM (1948) as a previously existing symbol. Some other new symbols were introduced in this chart. From the listed decisions, it is not clear when these were first approved, but prior to 1948.

    *The prefix micro- and its symbol µ were introduced in Resolution 12 of the 11 CGPM (1960).

    *The unit name micron and its standalone symbol µ were both abrogated by Resolution 7 of the 13 CGPM (1967/8), reserving the symbol only as a prefix.

    The micron was previously accepted both as a pre-SI metric unit and an SI unit. However, the usage has been obsolete, officially abrogated, since 1968. In the article's original list, the use of the unit name micron (and various spellings) seems just as a wrong as using its former standalone symbol. Only 75 µm should be used. If the spelled-out word is used, I suppose all the national variations are required. In this sense, the approved symbols are vastly superior to words.

    I could not find an example of a sheet protector, but in the US we mark thickness of plastic trash bags as shown in the attached image (other brands are similar):,r:2,s:0,i:96&iact=rc&page=1&tbnh=195&tbnw=258&start=0&ndsp=9&tx=86.66668701171875&ty=161.66668701171875


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