# 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:** 3
**Author:** ![Bert\_Nobbins](https://avatars.discourse-cdn.com/v4/letter/b/aeb1de/32.png) [@Bert\_Nobbins](https://boards.straightdope.com/u/Bert_Nobbins)\ **Post date:** [June 14, 2020, 2:43pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/41 "2020-06-14T14:43:38Z")
> [@Tabco](#): > > Decibels are measured on a logarithmic scale, so the wide range of meaningful values (in nature) can be indicated with a relatively compact range of numerical outputs, precluding the need for a series of prefixes that indicate magnitude. 20 decibels has ten times the power of 10 decibels, and 30 decibels has 100 times the power, and so on. This is just my guess as to why prefixes are not often used with decibels. This is right. The logarithmic nature of dBs means that a huge variation can be described without using prefixes. For example, when measuring sound level, 0 dB is the threshold of hearing, while 130 dB is ‘instant ear damage’. The smallest change in level detectable by the ear is about 1 dB. There is just no need for mdB and I have never come across such a unit. ---
**Author:** ![Novelty\_Bobble](https://avatars.discourse-cdn.com/v4/letter/n/a3d4f5/32.png) [@Novelty\_Bobble](https://boards.straightdope.com/u/Novelty_Bobble)\ **Post date:** [June 14, 2020, 2:59pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/42 "2020-06-14T14:59:28Z")
> [@Senegoid](#): > > I think you didn’t read the problem very carefully. Note that most of the measures are given in feet, but the distance to the airport is given in nautical miles. You can’t just change _all_ the measures to meters or kilometers. OK, so if a similar problem were given in metres and kilometres…how is that any harder? > [@](#): > > Furthermore, the problem as given is a real problem. The specific distances are all realistic, as are the choices of unit of measure to use. If you change, say, 5000 feet of altitude to 5000 meters, you are now at about 15000 feet, so the problem is not whether you can reach any nearby airport, but how much supplemental oxygen you should be breathing. so call it a 1000m or 1500m instead and take the problem of oxygen out of the equation. Seeing as I did read your post carefully I can tell you that oxygen was not mentioned in your orginal problem. > [@](#): > > And anyway, the point was that nautical miles are easier to work with than statute miles. That may be the case, and you seem to be suggesting that it is in part due to neat rounding to appx 6000 ft. Well, as luck would have it a kilometre is already defined as an exactly round 1000m and that would make the vast majority of calculations even easier. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 14, 2020, 3:28pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/43 "2020-06-14T15:28:04Z")
> [@DPRK](#): > > A milligram of water _is_ about 1 cubic millimeter, so what do you mean here? Anyway you can’t massage units in such a way as to take away the power of 3 in [unit of volume] = [unit of length][sup]3[/sup], so not clear what extra smoothing is possible. when you use different prefixes for the same type of measure. e.g. 1 cubic **centi** meter of water is 1 **milli** liter. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [June 14, 2020, 5:49pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/44 "2020-06-14T17:49:32Z")
> [@jz78817](#): > > when you use different prefixes for the same type of measure. e.g. 1 cubic **centi** meter of water is 1 **milli** liter. I think it’s more or less clear from **Schnitte** ’s last post, but your example is a little misleading because the bolded prefixes are not attached to the same type of measure: dimension(meter) = L, but dimension(litre) = L³ . ---
**Author:** ![Tim\_T-Bonham.net](https://avatars.discourse-cdn.com/v4/letter/t/46a35a/32.png) [@Tim\_T-Bonham.net](https://boards.straightdope.com/u/Tim_T-Bonham.net)\ **Post date:** [June 14, 2020, 6:42pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/45 "2020-06-14T18:42:50Z")
> [@Shalmanese](#): > > b) Are there any other units where deci- is (one of) the most commonly used prefix? In English-speaking countries, the height of horses is measured in ‘hands’. A ‘hand’ is defined as 4 inches, which happens to be very close to a deci-meter (3.937008 inches) – only a 1.5% difference. (For even the record tallest horse, it’s a very minor difference: 20½ hands vs 21 decimeters). So back when it was looking like UK/USASA/Australia would switch to metric measurements, the decimeter was suggested as the appropriate measurement for horses’ height. Because it would be so easy for horse people – almost no adjustment at all. But that never happened. ---
**Author:** ![Ruken](https://avatars.discourse-cdn.com/v4/letter/r/f475e1/32.png) [@Ruken](https://boards.straightdope.com/u/Ruken)\ **Post date:** [June 14, 2020, 11:20pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/46 "2020-06-14T23:20:18Z")
Re: mmHg, obviously you can measure that with a simple manometer made from a U-tube and a ruler. But our Schlenk lines were pulling 40 millitorr. Before we bought digital ones we had some tilty thing with different diameter tubes for more precise, low-pressure measurements. I cannot remember the name. A good reading is important for vacuum distillations. And we definitely said “millitorr”. ---
**Author:** ![Sunspace](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/sunspace/32/1250_2.png) [@Sunspace](https://boards.straightdope.com/u/Sunspace)\ **Post date:** [June 15, 2020, 1:13am UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/47 "2020-06-15T01:13:57Z")
> [@mixdenny](#): > > 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 What, pascals too good for you? 🙂 And what happens if you’re measuring vacuum on the moon or in space? Measurements of millimetres of mercury will be off because the local weights will be different. ---
**Author:** ![Civil\_Guy](https://avatars.discourse-cdn.com/v4/letter/c/d78d45/32.png) [@Civil\_Guy](https://boards.straightdope.com/u/Civil_Guy)\ **Post date:** [June 15, 2020, 2:42am UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/48 "2020-06-15T02:42:48Z")
Oh, let’s confuse this even more. There’s a metric unit for pressure called a bar, equals 100 kilopascals, and one bar is close to regular atmospheric pressure at sea level – okay, it’s really the pressure at 15 deg C, 111 m elevation, per Wikipedia. So weather forecasts often use millibars, because 1000 mbar (or thereabouts) is easy enough to work with. I’d guess that ‘milli’ is the only prefix that works here. That said, bar is not an ‘official’ metric unit. ---
**Author:** ![GMANCANADA](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gmancanada/32/2837_2.png) [@GMANCANADA](https://boards.straightdope.com/u/GMANCANADA)\ **Post date:** [June 15, 2020, 5:01am UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/49 "2020-06-15T05:01:07Z")
**@Schnitte** > [@](#): > > 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. You missed the most important one of all: “An area “some multiple” of the size of Rhode Island” WTF is that??? Does anyone outride of RI conceptualize it? > [@](#): > > Southern California fires now bigger than New York City, 33% the size of Rhode Island … > **[Southern California fires now bigger than New York City, 33% the size of...](https://www.ocregister.com/2017/12/12/southern-california-fires-now-bigger-than-new-york-city-33-the-size-of-rhode-island/)** > > The December fires of Southern California have burned an area that totals one-third the size of Rhode Island. ---
**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 15, 2020, 7:21am UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/50 "2020-06-15T07:21:41Z")
> [@Civil\_Guy](#): > > Oh, let’s confuse this even more. There’s a metric unit for pressure called a bar, equals 100 kilopascals, and one bar is close to regular atmospheric pressure at sea level – okay, it’s really the pressure at 15 deg C, 111 m elevation, per Wikipedia. So weather forecasts often use millibars, because 1000 mbar (or thereabouts) is easy enough to work with. I’d guess that ‘milli’ is the only prefix that works here. That said, bar is not an ‘official’ metric unit. The bar is also used in diving, because, conveniently, ten metres of pressure head of water corresponds to one bar of pressure. So at a depth of 30 metres, pressure is 4 bar (one bar from atmospheric pressure, plus one bar for each ten metres you’re going down). When a watch is labelled as waterproof up to, say, 50 metres, all it means is that it has been tested to withstand pressure up to 6 bar. ---
**Author:** ![Remember\_me](https://avatars.discourse-cdn.com/v4/letter/r/82dd89/32.png) [@Remember\_me](https://boards.straightdope.com/u/Remember_me)\ **Post date:** [June 15, 2020, 7:44am UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/51 "2020-06-15T07:44:25Z")
> [@DPRK](#): > > I think it’s more or less clear from **Schnitte** ’s last post, but your example is a little misleading because the bolded prefixes are not attached to the same type of measure: dimension(meter) = L, but dimension(litre) = L³ . No, a cubic centimeter is L³ not L. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [June 15, 2020, 7:52am UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/52 "2020-06-15T07:52:07Z")
> [@Remember\_me](#): > > No, a cubic centimeter is L³ not L. It’s (centimeter)³, not centi(meter)³, was my point. Liters of water and kilograms will scale the same way, though: 2 l weigh 2 kg ---
**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 15, 2020, 8:11am UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/53 "2020-06-15T08:11:04Z")
As for the initial question, I have only ever heard Becquerel (Bq), the SI unit of radioactivity, used with prefixes such as kilo- or mega-. That’s because the Bq is defined as one decay per second, which is very little for radioactive substances, so pretty much all applications (maybe outside basic research) will be orders of magnitude above that. Ironically, the predecessor unit, the Curie (Ci), was suffering from the opposite problem: 1 Ci (equivalent to 37 GBq) was so much that it would often have to be prefixed with centi- or milli- prefixes. ---
**Author:** ![Quercus](https://avatars.discourse-cdn.com/v4/letter/q/7ab992/32.png) [@Quercus](https://boards.straightdope.com/u/Quercus)\ **Post date:** [June 15, 2020, 12:20pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/54 "2020-06-15T12:20:45Z")
> [@MrDibble](#): > > “Cubic metre” may not be common because “kilolitre” exists. My water bill is in kL, not m[sup]3[/sup] Really? I was going to nominate Liter for the OP, since I can’t recall ever seeing liter with any prefix other than milli- (except perhaps in a general way “in the microliter range”). Now, 'round here water bills and such will be in cubic feet or gallons (or Million Gallons, for big amounts) ---
**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 15, 2020, 12:27pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/55 "2020-06-15T12:27:50Z")
> [@Quercus](#): > > Really? I was going to nominate Liter for the OP, since I can’t recall ever seeing liter with any prefix other than milli- (except perhaps in a general way “in the microliter range”). > > Now, 'round here water bills and such will be in cubic feet or gallons (or Million Gallons, for big amounts) I’ve never seen kilolitre either; around here, that volume is usually called a cubic metre (and billed as such on water bills). The output of German breweries, however, is traditionally measured in hectolitres. ---
**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 15, 2020, 1:25pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/56 "2020-06-15T13:25:55Z")
Liter is quite often also used without any prefix at all, like a 2-liter bottle. ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 15, 2020, 1:30pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/57 "2020-06-15T13:30:50Z")
> [@Civil\_Guy](#): > > Oh, let’s confuse this even more. There’s a metric unit for pressure called a bar, equals 100 kilopascals, and one bar is close to regular atmospheric pressure at sea level – okay, it’s really the pressure at 15 deg C, 111 m elevation, per Wikipedia. So weather forecasts often use millibars, because 1000 mbar (or thereabouts) is easy enough to work with. I’d guess that ‘milli’ is the only prefix that works here. That said, bar is not an ‘official’ metric unit. I think they just try to avoid fractions or decimals when using units to present to the general public. ---
**Author:** ![Telemark](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/telemark/32/372_2.png) [@Telemark](https://boards.straightdope.com/u/Telemark)\ **Post date:** [June 15, 2020, 2:24pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/58 "2020-06-15T14:24:48Z")
I’ve only ever heard calorie paired with kilocalorie. Is there any other common usage? ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [June 15, 2020, 2:38pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/59 "2020-06-15T14:38:55Z")
> [@Schnitte](#): > > I’ve never seen kilolitre either; around here, that volume is usually called a cubic metre (and billed as such on water bills). The output of German breweries, however, is traditionally measured in hectolitres. I was somewhat amused when I looked at a label in the cargo area of a EU-market Ford Transit van which indicated some sort of capacity in “daN” (decaNewtons.) I looked into it a bit more and that was evidently the “lashing” capacity; i.e. the rated force the cargo hold-downs could take. surprised me that daN is a common measure for LC. ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [June 15, 2020, 2:45pm UTC](https://boards.straightdope.com/t/apart-from-decibels-are-there-any-other-metric-units-that-are-only-ever-used-with-a-single-prefix/855604/60 "2020-06-15T14:45:35Z")
> [@jz78817](#): > > I was somewhat amused when I looked at a label in the cargo area of a EU-market Ford Transit van which indicated some sort of capacity in “daN” (decaNewtons.) I looked into it a bit more and that was evidently the “lashing” capacity; i.e. the rated force the cargo hold-downs could take. surprised me that daN is a common measure for LC. I don’t know about industry lingo- but 1 kg weighs roughly 1 daN. That said, if you buy eg a carabiner, it’s always stamped with a rating of however many kN, a daN being way too little… [Previous 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) [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=4)