Problems with US spelling variants for writing metric

This week, Ronnie Cohen takes issue with an example of American exceptionalism.

Most metric prefixes and units are spelled the same way throughout the English-speaking world. However, there are a few notable exceptions where the Americans use different spellings from the rest of the English-speaking world. The exceptions are:

  • metre (US spelling: meter)
  • litre (US spelling: liter)
  • tonne (US spelling: ton) – this refers to the metric tonne of 1000 kg
  • deca- (US spelling: deka-) – a metric prefix meaning a factor of 10

While the US spellings are used by the Americans, the British spellings are used by all major English-speaking countries and the rest of the Commonwealth, the European Union (EU), the World Trade Organisation (WTO), International Standards Organisation (ISO), the North Atlantic Treaty Organisation (NATO), International Olympic Committee (IOC) and the International Bureau of Weights and Measures (BIPM).

This issue matters for use in legal contracts in all countries where international businesses operate. There are also implications for international websites and publishing where separate versions of common materials or information must be produced for American and non-American readers.

The spelling “metre” always refers to the fundamental unit of length in the metric system. According to the Oxford English Dictionary (OED), it comes from Old English, reinforced in Middle English via Old French “metre”, Latin “metrum” and originally from Greek “metron”, meaning measure. From this word, we derive words and their spellings related to the metric system and general measurement terms such as:

  • metric
  • metrical
  • metricate
  • metrology
  • metronome (OED: A musician’s device that marks time at a selected rate by giving a regular tick.)

All the words listed above are related to “metre” and are never spelled meter-, always metr-.

The meter is normally used for measuring devices in all parts of the English-speaking world. The names of all kinds of measuring device end in -meter. According to the OED, meter comes from Middle English, that in the sense of “person who measures”, it is derived from “METE” + “-ER”.

It is often useful to distinguish between units of lengths and measuring devices. The “Spelling metre or meter” document by Pat Naughtin gives some useful examples (see link at the bottom of this article). It is a standard feature of English spelling to use different spellings for words that sound the same to convey meaning (e.g. wait/weight, whole/hole, etc.). It is also a hallmark of the English spelling system to retain the original spellings for foreign words (e.g. double, paella, pizza, spaghetti, etc.). The distinction between the “metre” spelling for distance and the “meter” spelling for measuring devices is especially useful for distinguishing between micrometre for a millionth of a metre and micrometer, an instrument for measuring extremely small distances. They are even pronounced differently. Micrometre is pronounced with emphasis on the first syllable whereas micrometer is pronounced with emphasis on the second syllable.

According to the OED, the metric unit of volume or capacity, the litre, comes from French, alternative of “litron”, an obsolete measure of capacity, via medieval Latin, from Greek “litra”, a Sicilian monetary unit. The OED lists the noun “litreage” as a derivative word of litre, interestingly with no variant spelling (i.e. “literage” spelling does not exist).

The “tonne” spelling is only used for the metric tonne, a weight equal to 1000 kg. The “ton” spelling is normally used for various types of non-metric tons. Some relate to mass and others relate to volume or capacity. The OED lists the following tons for which the “ton” spelling is used:

  • long ton
  • short ton
  • displacement ton
  • freight ton
  • net ton or register ton
  • gross ton

Each item in the list has a different meaning. The Americans also use the “ton” spelling for the metric tonne. When they write “ton”, they also need to write “metric” before “ton” to distinguish between the metric tonne and other tons. While the Americans do not use the “tonne” spelling, they still maintain the distinction between the “ton” and “tun” spellings. The OED lists “ton” as a word of Middle English origin and a variant of “tun” and says that both spellings are used for the container and the weight. If the Americans wanted to go for a phonetic spelling for the metric tonne, they would surely have opted for “tun”, which already exists as a valid English spelling, albeit used for other meanings. The “tun” spelling is used for large beer and wine containers and also for an imperial capacity measure equal to 4 hogsheads.

I did a quick online search to find out what other words ended in -onne then looked them up in the OED. I found the following entries in the OED:

  • chaconne (pronounced sha-kon)
  • cretonne (pronounced kre-ton)

For these words, there is no US variant spelling.

The “deca-” prefix does not just exist in the metric system. The “deca-” prefix, or “dec-” before a vowel, is a common English prefix used in many words for ten or for having ten. I found several examples of this prefix in the OED as shown in the table below:

Word with Dec-/Deca- Prefix OED Definition of Word
decade A period of ten years.
decagon A plane figure with ten straight sides and angles.
decahedron A solid figure with ten plane faces.
decalitre A metric unit of capacity, equal to 10 litres.
Decalogue The Ten Commandments
decametre A metric unit of length, equal to 10 metres.
decapod A crustacean of the order Decapoda, with five pairs of walking legs (i.e. with ten legs), such as a shrimp, crab, or lobster.
decastyle (of a temple or portico) having ten columns
decasyllabic (of a metrical line) consisting of ten syllables
decathlon An athletic event in which each competitor takes part in the same ten events.

The only spellings I found in the OED starting with “deka-” were the US spellings “dekaliter” for decalitre and “dekameter” for decametre. According to the OED, the Americans also use “decaliter” and “decameter” spellings and also use “dkl” and “dkm” abbreviations for decalitre and decametre respectively. These abbreviations are not recognised or accepted by the BIPM. These abbreviations are presumably used by the Americans as a result of their use of the non-standard “deka-” prefix. Only “dal” and “dam” are accepted symbols for decalitre and decametre respectively. For all the other words in the table above, there is no variant “deka-” spelling. Hence, for consistency, it makes sense for the Americans to standardise on the use of the “deca-” prefix and abandon the “deka-” prefix.

Variant US spellings are based on the ideas of Noah Webster, the original author of the American dictionary that bears his name. The Americans went their own way in terms of spellings, probably to differentiate their newly independent country from the British and to help the American publishing industry. While Americans do not accept the -re ending for metre and litre, they accept this ending for numerous other words such as acre and ogre and to differentiate between timbre/timber. Here, I made the case for the Americans to use the standard spellings for metric units used by the rest of the English-speaking world and virtually all international organisations. It is not clear to me what they gain by using separate spellings from the rest of the world. However, it has implications for international businesses. They would need to produce separate labelling, manuals, web pages, contracts and other materials for the Americans and the rest of the English-speaking world. At Pat Naughtin has pointed out, the British (and international) spellings for metric units are universally accepted but the American spellings are not. In markets where they are not accepted, that could make contracts for international businesses operating in these markets null and void.

Further reading:

6 thoughts on “Problems with US spelling variants for writing metric”

  1. The problem of language diversion is common to all colonial powers and their former colonies. Relative to other colonial powers, the UK and its Commonwealth have minimized that diversion among members of the Commonwealth, but the US is not a member. I see little hope of general reconciliation of British and American English; no one has ever agreed to a commission charged with such a task. In the Portuguese language, such a commission was formed and they settled on Brasilian Portuguese over Continental Portuguese, so there might be an element of “be careful what you wish for.” However, if you count the entire Commonwealth, you have us well out-numbered.

    It would not be the end of the world if we changed just the words which are part of the metric system and kept our other differences. However, you would have to convince official channels to change their guidance. We are TAUGHT to spell it in a way you consider incorrect. To the degree the government can direct such things, they direct us to do so.

    NIST interprets the SI for the USA via the authority of Secretary of Commerce as charged by Congress. They “prefer” the American spellings as stated officially in NIST SP 330. However, they seem to regard the alternate settings as “acceptable,” I don’t think they have the power to forbid them. I would further note that the SI Brochure mentions these spelling differences in the Foreword and does not seem overly concerned by them. The Style Manual of the US Government Printing Office requires the American spellings in all official documents (we have used them since the Metric Act of 1866).

    Webster defines “metre” simply as the British spelling of meter, and defines the unit of length under the meter spelling.

    A few picky items:
    *We also “prefer” the “L” symbol for liter/litre
    *Metric tonne is redundant as tonne refers only to a mass of 1000 kg, but metric ton is required to avoid confusion with other tons.
    *The only symbol for deca/deka is “da.” Random, made-up abbreviations are not allowed in the SI. The abbreviation dk might be some obsolete symbol. I have never seen it used, but I admit Webster does show it without a comment that it is incorrect; however, they show the correct symbol in articles on dekagram (dag), etc. Certainly, NIST does not allow dk.
    *Quantities should be specified using numeric symbols and unit symbols, not spelled out words, so I am not sure how serious the spelling of unit words is in contracts. (only lawyers think they add clarity by spelling out long numbers.)

    I prefer the metre and meter having the EXACT same length to the gallon (or pint) using the same word and different definitions in our respective countries. We would be better focused on completing metrication than a spelling bee. Those advocating the metrication of the US need to speak with a unified voice, and I believe that means following the metric guidance of NIST. We can’t have the government and individuals speaking or writing with different words. If you convince NIST to switch, I’ll switch.


  2. The one thing that has always struck me is that we use ‘metre’ as a unit to measure but ‘meter’ for devices to measure. We tend to write ‘gas meter’ and not ‘gas metre’ for instance.

    Now, gas tends to be measured cubic metres so there is some kind of link. Electricity is not measured in metres, however, and yet we write ‘electricity meter’.

    I am not proposing to harmonise these spellings (I think) but it is definitely inconsistent.


  3. It’s all about consistency. When you start a proof reading job, you need to ask if US or British English is required. I realise you can set the PC spell check, but there’s a bit more to it than that.
    For a future article, may I suggest one on metric/USCS term abbreviation.
    Jack, the Japan Alps Brit


  4. Someone once commented that if the English language were a company, most of the shares in the company would be held by the Americans as the American population vastly outnumbers that of other individual English-speaking countries. As a Brit, I find some American spellings of English words ghastly, e.g. plow, nite and thru. But I don’t really see how pressure can be brought on Americans to use the spellings of English words that the rest of the English-speaking world uses. It is not only the spelling of words that differs between Britain and the USA, use of grammar does too. But the English-speaking countries are strewn around the world, and with various influences impacting on them they have developed in their own ways, with alternative spellings and accents. However, the above article is concerned with the more specific issue of the spelling of the names of metric units, for which it seems only the Americans use certain spellings that diverge from those used in the rest of the English-speaking world. It is odd, I admit, to see the name of the basic unit of measurement in the metric system, the metre, spelt in the same way as a measuring device, a meter, both being spelt ‘meter’ in the USA. I feel the same way about litre versus liter and the other examples given above. But I cannot really say it grates on me. I am more bothered when I see pre-metric units of measurement still being used as primary units in the USA. I think I would go as far as to say that, if the USA were to join the rest of the modern world and fully implement the metric system for all purposes, I would forgive the minor indiscretion of a few divergent spellings, for which presumably they have their reasons. The American military does use metric and, I believe, soldiers refer to distances in kilometres as so-many ‘kays’ – a plural letter ‘k’ for kilometre. I don’t find this particulary elegant, but on the battlefield brevity is probably of the essence. English speakers in particular do seem to like to localise words. Perhaps the divergent American spellings of certain metric units are an illogical, but otherwise harmless example of such localisation.


  5. In recent years I’ve become very comfortable with the differences in UK and US English (and also those with Australia, NZ, Canada etc), working in a global team I’ve learned that spelling, grammar and even well used phrases have much the same history as the measurment systems that the Brits took to the colonies hundreds of years ago.

    Having worked with somebody who once studied languages some years ago I came to learn that dropping the “u” from words spelled “ou” (color/colour) or using “ze” instead of “se” at the end of words were things we did even here in Britain not so long ago, I was also told “fall” instead of “autumn” was common here in past centuries.

    Given that, as has been pointed out elsewhere, many countries have their own names for metric measures the swapping of “re” and “er” at the end of some names (as with many other words) seems to me like a trivial argument given the bigger picture.

    As much as it irks me to see KG, Kilo or Kgs in supermarket displays, so long as the supplemental imperial indications aren’t there it at least means that somebody has tried. In the same manner I would rather see a “2 Liter” Coca Cola bottle in a Los Angeles gas station than a “42 FL OZ” Pepsi because despite the spelling difference very few people are going to be mislead by what is in the Coca Cola bottle.

    Now if you’re writing international treaties or contracts there is clearly a very good reason for getting the spelling correct, knowing how lawyers and politicians love looking for loopholes, but again knowing that the source language is American English should surely be enough that this becomes a non issue as there are likely to be enough other differences as it stands.

    Frankly, the day I visit the US and see a gas station selling in $/Liter I will be overjoyed.


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