# Apart from decibels, are there any other metric units that are only ever used with a single prefix? **URL:** \ **Category:** Factual Questions\ **Created:** [June 13, 2020, 2:29pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604 "2020-06-13T14:29:54Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Shalmanese](https://avatars.discourse-cdn.com/v4/letter/s/45deac/32.png) [@Shalmanese](https://boards.straightdope.com/u/Shalmanese)\ **Post date:** [June 13, 2020, 2:29pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/1 "2020-06-13T14:29:54Z")
We never talk about bels or centibels or millibels, everything is always expressed in decibels for some reason. a) Are there any other metric units that have this same strange quirk and b) Are there any other units where deci- is (one of) the most commonly used prefix? I know deciliters are used occasionally in Europe for certain things but it’s rare to think of any other units where deci- is ever used. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 13, 2020, 2:34pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/2 "2020-06-13T14:34:24Z")
You’ll never see area measured in ares, or kiloares, or centiares, only in hectares. I half suspect that the “are” was back-formed because they wanted a unit of the same order of magnitude as “acre”, and they put a “hecta” in that unit because it’s the area of a square 100 m on a side (making it 10,000 square meters). ---
**Author:** ![Mark\_Finn](https://avatars.discourse-cdn.com/v4/letter/m/34f0e0/32.png) [@Mark\_Finn](https://boards.straightdope.com/u/Mark_Finn)\ **Post date:** [June 13, 2020, 3:06pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/3 "2020-06-13T15:06:11Z")
Does anyone use the “Stere” (one cubic metre)?. Cubic metres and centimetres (or "cc"s) seem to be the only units commonly used for volume. If I’m not mistaken, one stere (or cubic metre) is equal to one million cc’s. (one light year is equal to 9.46 petametres) 🙂 (apparently the stere is used in Europe for volumes of firewood) ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [June 13, 2020, 3:11pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/4 "2020-06-13T15:11:59Z")
> [@Mark\_Finn](#): > > Does anyone use the “Stere” (one cubic metre)?. The water company, when they bill you. I doubt you only used a few cc… ---
**Author:** ![racer72](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/racer72/32/3075_2.png) [@racer72](https://boards.straightdope.com/u/racer72)\ **Post date:** [June 13, 2020, 3:24pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/5 "2020-06-13T15:24:24Z")
> [@DPRK](#): > > The water company, when they bill you. I doubt you only used a few cc… My water bill in measured in cubic feet. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [June 13, 2020, 3:25pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/6 "2020-06-13T15:25:38Z")
Not metric, but the CGS unit centi-poise is commonly used for kinematic viscosity. It’s abbreviation is cP. It maybe because the kinematic viscosity of water is around 1 cP at ambient conditions. ---
**Author:** ![Colibri](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/colibri/32/1841_2.png) [@Colibri](https://boards.straightdope.com/u/Colibri)\ **Post date:** [June 13, 2020, 3:40pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/7 "2020-06-13T15:40:06Z")
The milli-Helen is the unit of beauty sufficient to launch one ship. I have never heard of any other prefix used with Helens. ---
**Author:** ![Arkcon](https://avatars.discourse-cdn.com/v4/letter/a/96bed5/32.png) [@Arkcon](https://boards.straightdope.com/u/Arkcon)\ **Post date:** [June 13, 2020, 4:11pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/8 "2020-06-13T16:11:52Z")
I don’t think degrees of temperature are particularly useful by any units other than centigrade. But I didn’t come up with that aphorism: [1643: Degrees - explain xkcd](https://www.explainxkcd.com/wiki/index.php/1643:_Degrees) ---
**Author:** ![Shalmanese](https://avatars.discourse-cdn.com/v4/letter/s/45deac/32.png) [@Shalmanese](https://boards.straightdope.com/u/Shalmanese)\ **Post date:** [June 13, 2020, 4:15pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/9 "2020-06-13T16:15:36Z")
> [@Arkcon](#): > > I don’t think degrees of temperature are particularly useful by any units other than centigrade. But I didn’t come up with that aphorism: [1643: Degrees - explain xkcd](https://www.explainxkcd.com/wiki/index.php/1643:_Degrees) Huh, I had no idea a centigrade was 1/100th of a gradian! ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [June 13, 2020, 4:20pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/10 "2020-06-13T16:20:23Z")
CGS units are metric. The “Metric System” is an umbrella that encompasses CGS, SI, and a few other related units. For instance, “mm of mercury” can be used as a “metric unit of pressure”, even though it’s not CGS nor SI. Come to think of it, that’s another one for this thread. Nobody ever measures pressure in centimeters of mercury, or micrometers of mercury, or whatever. If you’re in an application where mmHg aren’t good enough, then you’re probably using pascals (possibly with scientific notation or a prefix). ---
**Author:** ![Mark\_Finn](https://avatars.discourse-cdn.com/v4/letter/m/34f0e0/32.png) [@Mark\_Finn](https://boards.straightdope.com/u/Mark_Finn)\ **Post date:** [June 13, 2020, 4:20pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/11 "2020-06-13T16:20:44Z")
> [@Arkcon](#): > > I don’t think degrees of temperature are particularly useful by any units other than centigrade. But I didn’t come up with that aphorism: [1643: Degrees - explain xkcd](https://www.explainxkcd.com/wiki/index.php/1643:_Degrees) It’s 285 degrees Kelvin outside now - a high of close to 300 degrees later today. 🙂 ---
**Author:** ![F.U.Shakespeare](https://avatars.discourse-cdn.com/v4/letter/f/aca169/32.png) [@F.U.Shakespeare](https://boards.straightdope.com/u/F.U.Shakespeare)\ **Post date:** [June 13, 2020, 4:20pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/12 "2020-06-13T16:20:58Z")
> [@Shalmanese](#): > > We never talk about bels or centibels or millibels, everything is always expressed in decibels for some reason. > > a) Are there any other metric units that have this same strange quirk > > and b) Are there any other units where deci- is (one of) the most commonly used prefix? I know deciliters are used occasionally in Europe for certain things but it’s rare to think of any other units where deci- is ever used. I don’t know if this is officially part of the metric system. But in radio frequency (RF) engineering, power broadcast measurements in units of dBm (decibels referenced to one milliwatt) and dBw (decibels refernced to one watt) are common: 10log(1 watt) = 0 dBw = 30 dBm = 10log(1000 mw) ---
**Author:** ![Mark\_Finn](https://avatars.discourse-cdn.com/v4/letter/m/34f0e0/32.png) [@Mark\_Finn](https://boards.straightdope.com/u/Mark_Finn)\ **Post date:** [June 13, 2020, 4:54pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/13 "2020-06-13T16:54:52Z")
There is an Imperial measurement that is used worldwide - in metric regions as well as non-metric. The knot. Aircraft and ships seem to always use it. 1.15078 mph. 1.852 km/hr. ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [June 13, 2020, 4:58pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/14 "2020-06-13T16:58:05Z")
> [@Mark\_Finn](#): > > Does anyone use the “Stere” (one cubic metre)? Every audio system I have ever bought was in stereo. ---
**Author:** ![mixdenny](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mixdenny/32/2962_2.png) [@mixdenny](https://boards.straightdope.com/u/mixdenny)\ **Post date:** [June 13, 2020, 5:01pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/15 "2020-06-13T17:01:49Z")
> [@Chronos](#): > > Come to think of it, that’s another one for this thread. Nobody ever measures pressure in centimeters of mercury, or micrometers of mercury, or whatever. If you’re in an application where mmHg aren’t good enough, then you’re probably using pascals (possibly with scientific notation or a prefix). Microns of mercury is a common measurement for intermediate vacuum systems. My Kinney KC-5 can pull down to 25 microns. (Anyone need a vacuum pump?) In a vacuum system in that range we usually said micron instead of Torr. Lower then 1 micron (10 -3 Torr) it was always Torr. But seldom milliTorr, we always used the -3, -6 or whatever. A shorthand way of referring to a high vacuum system might be, 'It can pull down to the -6 range". Dennis ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [June 13, 2020, 5:03pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/16 "2020-06-13T17:03:10Z")
> [@Mark\_Finn](#): > > It’s 285 degrees Kelvin … Degree is not used with Kelvin. “ The 13th CGPM changed the unit name to simply “kelvin” (symbol: K).[13] The omission of “degree” indicates that it is not relative to an arbitrary reference point like the Celsius and Fahrenheit scales ” > **[Kelvin](https://en.m.wikipedia.org/wiki/Kelvin)** > > The kelvin, symbol K, is a unit of measurement for temperature. The Kelvin scale is an absolute scale, which is defined such that 0 K is absolute zero and a change of thermodynamic temperature T by 1 kelvin corresponds to a change of thermal energy kT by 1.380649×10−23 J. The Boltzmann constant k = 1.380649×10−23 J⋅K−1 was exactly defined in the 2019 redefinition of the SI base units such that the triple point of water is 273.16±0.0001 K. The kelvin is the base unit of temperature in the In Hi... ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [June 13, 2020, 5:15pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/17 "2020-06-13T17:15:04Z")
> [@Mark\_Finn](#): > > There is an Imperial measurement that is used worldwide - in metric regions as well as non-metric. > > The knot. > > Aircraft and ships seem to always use it. 1.15078 mph. 1.852 km/hr. This is related to 360 degrees in a circle (does that count as “imperial”?), each of which is divided into 60 minutes. That raises the question if anyone uses “millidegrees”. Milliradians, sure. Minutes and seconds, definitely. But who uses centidegrees or some other decimal fraction? ---
**Author:** ![CookingWithGas](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/cookingwithgas/32/485_2.png) [@CookingWithGas](https://boards.straightdope.com/u/CookingWithGas)\ **Post date:** [June 13, 2020, 6:41pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/18 "2020-06-13T18:41:33Z")
> [@Mark\_Finn](#): > > Does anyone use the “Stere” (one cubic metre)? Every audio system I have ever bought was in stereo. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [June 13, 2020, 6:49pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/19 "2020-06-13T18:49:22Z")
> [@Mark\_Finn](#): > > There is an Imperial measurement that is used worldwide - in metric regions as well as non-metric. > > The knot. > > Aircraft and ships seem to always use it. 1.15078 mph. 1.852 km/hr. What does that have to do with the OP’s question? Incidentally, as **DPRK** pointed out, the knot is not (pun intended) an imperial unit. It is one nautical mile per hour, and the nautical mile was defined as one minute of arc (1/60 of a degree) along the Earth’s meridians (or one minute of difference in latitude). This has the charm that differences in coordinates can be more easily converted into distance in nautical miles. It is also the reason why nautical charts do not indicate a bar scale. Instead, they indicate degrees and minutes of latitude and longitude, so if you want to know how much a nautical mile is on your map, just look at the left-hand side where you can see the latitudes. ---
**Author:** ![Schnitte](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/schnitte/32/9033_2.png) [@Schnitte](https://boards.straightdope.com/u/Schnitte)\ **Post date:** [June 13, 2020, 6:59pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/20 "2020-06-13T18:59:13Z")
> [@Chronos](#): > > You’ll never see area measured in ares, or kiloares, or centiares, only in hectares. I half suspect that the “are” was back-formed because they wanted a unit of the same order of magnitude as “acre”, and they put a “hecta” in that unit because it’s the area of a square 100 m on a side (making it 10,000 square meters). True, and the way area is commonly reported in the media really bugs me. I hate it when I read news like “766,000 hectares of forest were destroyed in the 2018 California forest fire season”. Give me the same data in square kilometres (7,660), and I can easily visualise it - as a rectangle 76.6 kilometres one side and 100 kilometres the other, which are distances I can relate to. Much more intuitively graspable than 766,000 hectares. The only thing that’s worth than that is if area is stated in “football fields”. For some reason, journalists seem to believe their readers are too dumb to understand square kilometres, but can intuitively relate to an area of so-and-so-many thousand football fields. And I have no clue how many square metres a “journalistic football field” is supposed to be equal to. [Next page](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604.md?page=2)