Why does the Star Trek franchise (produced in the USA) use Celsius for temperature and other units from SI, rather than Fahrenheit and units from the imperial system (still widely used in USA)? Eventually, as per Paul D. Waite's comment, the question can be, why don’t they use Kelvins?

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    "The metric system is the tool of the devil! My car gets forty rods to the hogshead and that's the way I likes it." Abe Simpson.
    – Kreann
    Commented Dec 14, 2014 at 17:10
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    Why would it use Farenheit? Commented Dec 14, 2014 at 18:51
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    We're slowly converting to metric, just as we're slowly getting over our reluctance to learn other languages. Work in progress, some assembly required. Batteries not included.
    – Joe L.
    Commented Dec 14, 2014 at 18:55
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    The real question is why don’t they use Kelvins? Commented Dec 14, 2014 at 20:50
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    Technically the US doesn't use the imperial system, the US uses 'US Customary Units', which is a very similar system but with notable differences such as the definition of the Gallon.
    – Pharap
    Commented Dec 14, 2014 at 22:30

11 Answers 11


Today, countries making up about 95% of the world's population use the metric system:

world map with USA, Liberia and Myanmar highlighted

The holdouts are the USA, Liberia, and Myanmar.

If the Earth is peacefully united and sends missions to the stars -- as is the case in Star Trek -- the overwhelming majority of people would be metric users. Simple democracy would lead to the metric system being adopted.

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    <comments removed> I understand being passionate about how people measure stuff, but comments aren't the place for discussing it.
    – user1027
    Commented Dec 16, 2014 at 15:35
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    USA was supposedly supposed to switch at the same time Canada did, it was kind of like a mutual agreement made between neighbors. Then USA backed out just after Canada had already commited itself. Now all our cars have to have fine print MPH in the dash, and our construction materials are all still in the old imperial system because our number one export is to the USA. Now Canada is stuck in a type of limbo, half way between both systems...
    – ShemSeger
    Commented Dec 16, 2014 at 18:31
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    Actually Myanmar (aka Burma) announced in 2013 of a full conversion to metric. That leaves only 2 countries!
    – Octopus
    Commented Dec 17, 2014 at 6:37
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    @NickT - we (the UK) uses miles for distance, but a lot of stuff is metric: weight (grams), volume (litres), temperature (celsius, aka centigrade). Actually, weight and height is a bit more complicated - food is sold in grams (or kilograms), and furniture etc is described in metres/cm but when people talk about their own weight and height they use stones/pounds and feet/inches. Commented Dec 17, 2014 at 11:19
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    @user14111 - I would assume the universal translator could handle basic unit conversions. Commented Jan 1, 2015 at 17:59

Short answer? People feel that the future is the metric system. It's more endorsed by the scientific community. Many nations have adopted it as a universal measure. Thus, in a farflung science-heavy future, the assumption is that people will be using metric units exclusively, the same reason futurists thought people would all be speaking Esperanto in the future as seen in the Harry Harrison books.

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    And yes, that's a TV Tropes link. Beware.
    – FuzzyBoots
    Commented Dec 14, 2014 at 17:09
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    You're on the right track, but the Esperanto comparison is not a good one -- hardly anyone speaks Esperanto, whereas 95% of the world's population uses metric. Commented Dec 14, 2014 at 17:24
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    @RoyalCanadianBandit: Some fads catch on better than others. :) I originally had a joke line at the end of my answer about how, instead, everyone speaks English, proven to be the superior universal language, but it seemed too much like flamebait.
    – FuzzyBoots
    Commented Dec 14, 2014 at 17:39
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    @trejder That's actually a pretty sane URL. As for the purpose of the site, it's an excellent documentation of literary tropes within a vast array of media. If you are at any point intending to write a story it is an invaluable resource.
    – Pharap
    Commented Dec 14, 2014 at 22:46
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    But be careful! Once you've clicked, you'll never stop...... Commented Dec 15, 2014 at 0:30

Because Star Trek is a show about a mission to explore space, and scientists -- yes, even in the United States -- use the metric system.

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    @Richard The common people uses mainly imperial system in their everyday. The longterm tendency goes into the direction of the metric system. If we extrapolate from the history of the last 200 years, I think a prediction of a world-wide metric system can be considered strong. And sci-fi films are based mainly on extrapolations (social and technical).
    – user38223
    Commented Dec 15, 2014 at 10:54
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    They come mostly from the US because the program is made in the US. It's made clear in the series that it's a United Earth type idea, though.... the assumption is that the crews are far more balanced than in the TV series. Or in short, don't take the TV show as directly indicative of the fictional environment.
    – Jon Story
    Commented Dec 15, 2014 at 10:55
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    I guess they come from the U.S., except for Chekov, Sulu, Uhuru, Spock, who are American actors representing Russia, Japan, Aftica, and Vulcan.
    – rbp
    Commented Dec 15, 2014 at 14:18
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    "Takei recalled Gene Roddenberry wanted the character to represent all of Asia, which symbolized the peace of the Trek universe in spite of the numerous wars in the continent." en.wikipedia.org/wiki/Hikaru_Sulu
    – rbp
    Commented Dec 15, 2014 at 17:54
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    Are any of those characters coming from the U.S., or coming from territory that was once the U.S.? I don't think there's much evidence that the U.S. still exists as a political entity in the Star Trek universe.
    – PersonX
    Commented Dec 16, 2014 at 3:25

You answered your question in the question - because Celsius is an SI unit (well it's not really, Kelvin is, but Celsius is just a constant offset so it is for the purposes of this question). There's no logic to a scientific organization in the future using anything other than what the scientific community use (Nasa used imperial for a while because it was US based).

Other people have mentioned the fact most of the world use Celsius, but this is irrelevant. While it's sensible for countries to use SI, even if no one used Celsius, it would still be adopted by any scientific organization. An example is acceleration, where no country (as far as I know) would quote acceleration in m/s^2 but that's what science uses.

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    And as a result of using imperial units crashed a $125 million space ship into mars; edition.cnn.com/TECH/space/9909/30/mars.metric. I'm wondering if thats when they went all metric
    – user20310
    Commented Dec 14, 2014 at 21:47
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    @user20310 It was an incorrect conversion between the two, not simply a result of using imperial units.
    – Izkata
    Commented Dec 14, 2014 at 22:00
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    Nitpick: it's a constant offset, not a "constant factor offset".
    – Eric Smith
    Commented Dec 15, 2014 at 9:24
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    What do the countries use to measure acceleration? (I don't use this at all in everyday live.) Commented Dec 15, 2014 at 9:58
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    @PaŭloEbermann In any scientific context, acceleration is measured in meters per second per second (a.k.a. meters per second-squared). In non-scientific context, "g"s (i.e., multiples of the acceleration due to gravity) are commonly used. For example, a racing driver or fighter pilot might talk about a "5g turn", meaning a turn involving five times the acceleration of gravity. Commented Dec 15, 2014 at 15:07

The Federation is a utopian society derived from Earth. Such a utopian future world would use a consistent and planned measurement system. Thus they use Celsius. Because it is logical and simple. One Celsius degree is the same as one Kelvin which is 1/100th of the total range from the freezing point to the boiling point of water (at 1 atmosphere pressure). Fahrenheit is much more complicated scale (see here).

Kelvin are much more unwieldy at the temperatures that we are accustomed to. Warm summer day is 298K or 25 degrees C. Note, the size of the Kelvin is set as the same as the degree Celsius. Kelvin just starts at 'absolute zero' which is -273.15 deg C.

So Celsius was probably chosen because it is consistent, logical, simple, yet relatable by average audience (Americans in the Sixties), and it was also 'futuristic' to non-scientists at the time ST was invented.

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    "Because it is logical..." (+1)! LOL! Do you have any Vulcan relatives? :>
    – trejder
    Commented Dec 19, 2014 at 6:44
  • Maybe...I am an analytical person, studied mechanical engineering and I work with computers. I like "logical". Always thought that the characters were archetypes, some of them out of proportion. Spock as the ultimate scientist, following logic like a cultmember. Bones as a grumpy old guy. Scotty as the epitome of an engineer (needs to drink more beer). Kirk as the dashing hero...women want him, men want to be him.
    – Xalorous
    Commented Dec 22, 2014 at 20:56
  • Good points, but if the units system were derived by scientists more advanced than those at the time of Napoleon, Kelvin would be used instead of Celsius. Celsius is a degree (sic) better than Fahrenheit, but of course still a historical artefact. Now we are stuck by using Celsius and Kelvin both as recognized metric units. Or Celsius should be (re)defined as Kelvin minus exactly 273.0000 .
    – Roland
    Commented Dec 23, 2014 at 22:40
  • In my old flat I updated my oven to read temperature in proper Kelvin. It's not that hard to get used to.
    – moopet
    Commented Mar 17, 2016 at 13:40

Here and there both systems are used - sometimes just I think because 'miles' and 'inches' are easier to grasp in the mind and feel more human. However look how metricated the whole mythos is at its core - from stardates to coordinates. Therefore it is very logical they should use Celcius as well.

Most importantly of all; Trek represents a utopian future where mankind has joined together without negative nationalism nor bigoted jingoism. In this single culture the sheer number of humans who do measure things in tens would massively outweigh those who don't. Logic - and therefore the metric system - would prevail through democracy just as @Royal says. Metric is also the measurement system of Science and Trek is a high Technocracy.

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    Whether the imperial system is more intuitive is probably a matter of what was the first thing you learnt. Sweden has been metric since looong before I was born, so in my lifetime there hasn't even been a remnant of older systems. And although I have a basic understanding of the imperial system, the metric system is more intuitive to me.
    – user36119
    Commented Dec 14, 2014 at 19:46
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    Excellent point @Sixth. Britain switched in the early Seventies. Huge improvement, trust me - and I have had pretty equal chunks of experience with both. I still think about distances in terms of feet and yards, though. Strangely the same is not true for all the other measures whether currency or Temp. I do not know why.
    – user38114
    Commented Dec 14, 2014 at 20:25
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    @SixthOfFour Couldn't agree more! In SI, Water freezes at 0 and boils at 100. Atmospheric pressure is exactly 1atm. 1J of energy is the work done in moving 1C charge through 1V. Avogadro number belongs to SI. One could use any SI unit and scale it as they wish just by multiplying with powers of 10 - no need to change names or switch units. Commented Dec 14, 2014 at 21:58
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    "sometimes just I think because 'miles' and 'inches' are easier to grasp in the mind and feel more human" That's not strictly true, it depends what you've be taught to use. All my life the rulers (the measuring implements, not monarchs) in my country have always had both inches and centimetres, but because I've never had to use inches and never been told to use them, I never do and they feel incredibly unnatural.
    – Pharap
    Commented Dec 14, 2014 at 22:51
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    I don't know where you're from, @GemmanAster, but around these parts people have different sized feet and thumbs
    – Jon Story
    Commented Dec 15, 2014 at 10:53

Gene Roddenberry was a visionary. I think he foresaw that future generations would be more likely to use metric units, which are already used by the scientific community (and by almost every nation on Earth outside the U.S.).

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    Though your answer looks pretty much like a comment than a full-blown answer, I must admit, that I like its simplicity (+1) :> However (since you're new to this society), please read carefully Help section on how to ask a good question and how to add a great answer. And next time try a little bit more elaborated answers. Or else, anti-comment-like-answers-maniacs will simply crucify you or send you to the next mission to Very Deep Space Something station! :>
    – trejder
    Commented Dec 19, 2014 at 6:47
  • thank you very much :D i love this site i just discovered
    – Rocket
    Commented Dec 19, 2014 at 17:51
  • Actually, US uses metric, mostly. Try the nuts and bolts on your car, they're probably metric if your car is < 20 years old. Main place US hasn't converted, is consumer products. But they all have metric measurements on them. And I saw a 500ml bottled drink yesterday. My first comment was to ask if it was imported. Nope. Pepsi is evidently trying expanding its metric sized packaging. Also, you'll find metric is taught in Science and Engineering classes in colleges and that those disciplines use metric wherever possible in industry as well. The military uses metric for many things also.
    – Xalorous
    Commented Dec 22, 2014 at 21:10
  • I'm Canadian so... i've been using metrics all my life ;)
    – Rocket
    Commented Dec 22, 2014 at 21:11
  • metric...almost every nation on Earth: the issue for Star Trek is what system would most likely be used by 'almost every civilization in the Universe'. Is it a general evolutionary advantage to have 10 fingers / toes to count with? If another intelligent species would have a power of two fingers, that would match more with Imperial, with a unit of length divided in 2 parts, or 4, 8, 16, 32 etc.
    – Roland
    Commented Dec 23, 2014 at 22:32

Star Trek is just a story. SI is just another future ideal world. The real world in fact produces a lot of incompatible systems, hard to use computers, etc., and uses imperial units in lots of places. I am talking here about the so-called metric world, e.g. The Netherlands. My bicycle has 28 inch wheels. Electronics goes in 19 inch racks. Spacing of integrated circuit leads are in 1/10 inch. (Ok, 1/10 is kind of metric.) Resolution of printers and photos is in dpi dots per inch. Examples of non-imperial, but also non-metric units used here: light year, oil production in barrels.

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    SI is not another future ideal world. SI stands for Système International, and is the basis for a unified system of measurement that is used by the scientific community. (And please, fix your Trak to Trek. Star Trak makes for very sad horta.) Commented Dec 19, 2014 at 8:36
  • Are racks 19 inches exactly? Or maybe 19.6 inches (approx 0.5 meter).
    – Xalorous
    Commented Dec 22, 2014 at 21:11
  • @Xalorous Are you kidding me :-) ? Dividing an inch measurement in ten parts??? As far as I know, as an unbeliever, you could have meant 19.625 inches. But as for your question: 19 inch racks are characterized by front panels of 19.00 inches wide.
    – Roland
    Commented Dec 23, 2014 at 22:10
  • @Xalorous 0.5 meter ... At Brown Boveri (Switzerland) I worked with 19 inch racks that were actually 22 inches wide. These were nice to stuff in more modules horizontally, probably like that we in Europe prefer A4 paper size because it is just a bit wider than Letter sized paper.
    – Roland
    Commented Dec 23, 2014 at 22:18
  • Rack units were defined by the EIA, which was/is an American organization. So, yes, as long as the U.S. still mixes metric and imperial units, the rest of the world will probably also have to mix the two, though to a lesser extent, and many fields still use SI exclusively even in the U.S. Commented Jan 10, 2015 at 6:33

I think the "universal translator" takes care of it, as does the specialized translators used for ships log entries etc.

If Spock were to use a cultural reference in his Officer's Log, and speak of "a hundred twenty eight squelm" in FedStandard (which is decendent from and rendered as English in the show) the metadata would automatically note the standard value in kelvin, and later when a sulfer-breathing admeral from Sarr reads it, it will be in his native language with the value in kelvin and a footnote explaining that the author likened it to the desert mesa whatever blooms are triggered, with links. Or, it may show a notation mapping to the normalized clement range of the author, so he knows without distraction if that is supposed to be hot or bitter cold or whatever. In the case of a human reading, Fahrenheit might be one of the configurable options of the normalized clemency perception scale.

Since Starfleet is primarily founded and organized by Terran and Vulcan world governments, whose to say SI is the end-all/be-all of measurements? They might use Vulcan-based Interplanetary Standard units.


Your question isn't entirely accurate. Star Trek uses imperial measurements. :)

In Star Trek, the original series, they use imperial. E.g. Spock tells Kirk a temperature in Fahrenheit, and at some point they both look at Mudd's data file and it gives his height in feet.

They also use metric, sometimes in the exact same episode for the same measurements (e.g. distance). It's a big mix.

From a production standpoint this is presumably because the writers at the time didn't put much thought in and just wrote what they know.


For scientific purposes metric is the accepted standard, so for those above the Enterprise (all of whom have some degree of scientific expertise) it would simply be natural. On top of that, astronomical units of measurement are based in the metric system for example, we use Km to measure near planetary distances, it's only when we get up to interplanetary distances that we start to measure in AU (the distance from the Earth to the Sun), but gigametres are also interchangeable here. As we continue increasing in size above parsecs we have the kiloparsec and megaparsec which are all metric units of measurement.

As for why they don't use Kelvin - Kelvin has a straight conversion of just being 0 Celsius + 273.15 so the two are interchangeable. We can assume that they use the two interchangeably as the scientific community does, so for ambient temperatures will refer to 25C rather than 298.15K but when referring to the very cold might use Kelvin. So they probably do use Kelvin but it's all based on context, for example I don't say that my walk to the kitchen is 0.003Km from my sitting room, instead I just say it's 3m.

  • This doesn't explain why they would use these measures.
    – Valorum
    Commented Sep 24, 2015 at 12:53
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    @Richard are you referring to why they would use metric? That's covered in the first paragraph, that for science (and astronomical units apply more directly) metric is the agreed standard.
    – Alex Deas
    Commented Sep 24, 2015 at 12:57
  • You've explained why some people in the real world use celcius/farenheit, not why the people in the trek universe use it.
    – Valorum
    Commented Sep 24, 2015 at 13:18

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