How common is the “deci” prefix in the metric system?

It seems like it should be fairly useful but it appears to be the bastard child of the metric system. However, I’m an American so my familiarity with usage of the metric system is decidedly limited.

decibels = yeah; decilitres = not so much; decimeters, decigrams, just nope.

But you could say the same (or more so) for deka and hecto. I mean, you’ve got hectares but when was the last time you ran into hectograms or hectometers? Or dekalitres or dekameters?

The ones that get all the attention are multiples of 1000, either up or down. Kilo and milli. And mega and micro.

Hectolitres is commonly used for the production of goods. We do a lot of work in analytics for the beverage alcohol industry and beer is measured in hL. Wine on the other hand is usually measured in 9L cases (750mL bottles x 12 per case).

True. Also hectares. They aren’t completely unheard-of, those hundred or ten prefixes, but as I said the most common ones are the step-ups of 1000 ( or one thousandth) of the previous major step.

My candidate for the absolute least used prefix is “myria”. I think it’s actually deprecated, in fact. It means 10,000 of the base unit. I remember it being taught to us back when I was in fifth grade when we had a chapter on the metric system.

In some European countries they measure drink sizes in deciliters. Other European countries use centiliters for the same thing.

A Reddit thread on the subject:

The decibel is not a metric or SI unit. Indeed it isn’t a single unit of measure. It is a ratio, and is thus itself unitless. It expresses the ratio of two power measurements. Those power measurements can, in principle, be of any unit, and are often not SI units. You can express different sorts of energy deliver using a dB based measure, but the measure needs to be qualified to a base level of power, and this base level differs from field to field. The most common thing is people using it as a measure of sound pressure. But there it is referenced to the very non SI value of 2 * 10-5 Nm-2. Metric but not very SI. Optical power is referenced to one milliwatt. So there is a double non SI there. Decibels of milliwatts.
The bel is the thing the deci refers to, and it is just the logarithm of the ratio.

Deciliter is very common for measuring liquids, either for serving or for cooking.

Here is a link to nearby brewery which sells beer by the dl.

From personal use in Slovakia:

  • centimeter is in common use
  • centiliter is rare, shot glasses would be marked as 5 cL
  • deciliter is the standard unit for beverages (glasses, cans, bottles)
  • decimeter is rare
  • dekagram is the standard unit for cooking and baking, is used when buying smaller quantities of produce (buy 40 “deka” of walnuts @ grocers)
  • hectoliter is standard when talking about production of alcohol and other drinks
  • hectare is standard when talking about larger areas (fields, forests)

Even though hectares are commonly used, I’m not sure you can count that as a use of the prefix hecta-. When was the last time you saw ares being used? In practice, the hectare itself is the unit of land area, rather than being a multiple of some other unit.

Not sure exactly how relevant this is, but I felt it’s worth mentioning that in some places, common purchasing units are expressed conversationally as fractions of a kilogram or a litre - for example in Spain, I observed people asking for medio kilo (half a kilo) of something rather than 500g. Quarter-kilo was also common; not sure about any other divisions

mg/dL (milligrams per deciliter) is used for some medical measures (blood glucose for example)


I think one important aspect to think of when analyzing frequency of usage is how often you encounter the “kind of thing” that it is suitable for measuring.

Similar to Slovakia in Norway recipes are full of deciliters for volumes, not only of liquids but for sugar and flour. Soda is usually labeled in liters these days, since 1.5 and 0.5 are the most common sizes sold. And I think the smaller bottles at some point changed to 0.33L from 33cL, but I know live in the US and don’t have any such bottles handy.

Unlike Slovakia “dekagrams” are not used, it’s either mg or kg in recipes, but the grocery stores will have some prices in kroner pr hg, especially at the deli counter.

Hectoliters are standard in a lot of fields with large volumes. But if you don’t work with such volumes you won’t be familiar with it.

It depends. Land is officially measured in m2. However, colloquially, everybody will refer to their backyard as being 4 ares.

I dispute the deka with a “k”, I suspect that to be a slav prefix, it rings a bell in my very hazy memories from Russian. The prefix you meant is I believe deca with “c”.

One I never understood as a child is “cuarto y mitad”, that is 375 g. My mother (German, presumably not familiarized with that sub-unit) never asked for that, but I heard it often from other women buying in the market. A quarter of a kg (250 g) and half that again (125 g), makes together 375 g. I finally remembered to check it, the internet is a know-it-all. Nice that you finally got me to remember to look it up.

I think part of the popularity of hectares as a land measurement unit is that they are not orders of magnitude different from the popular imperial/US customary acre unit that preceded it, and also because conversion is not difficult (1 hectare is quite closely approximate to 2.5 acres)

I have a glass Coca-Cola bottle, likely from Mexico, which proclaims a medio litro of soda.

Another common usage of “hecto” prefix is in German weather forecast: air pressure is usually given in hPa (with is the same as mbar). Standard atmospheric pressure is 1013.25 hPa.

We might predominantly use SI-units in Europe, but the common usage of prefixes tends to differ quite a bit between countries.

Meriam-Webster disagrees with you:

But Wikipedia agrees. And here is a list of all prefixes, and it lists deca and not deka. I use Merriam-Webster myself, but I doubt it is accurate in this case. How would such a doubt be settled in your view?

How about both are OK?