They are "technically correct" measurements since they are a valid prefix, and could be used if you wanted. but they are very infrequently used in any industry. Since most of the time measurements are better served by higher precision (just using Meters) or need no precision at all over long distance (switch to kilometers), no need for excess measurement types unless necessary
Well he asked about deca and hectometers, which are all larger-than meters.
But the same kind of rules apply below the decimal point as above it. We have millimeters (0.001 extreme precision), centimeters (0.01 high precision), and meters (1 low-ish precision). Decimeters (0.1) exist but are rarely used since both meters and centimeters can get the same result. Micro meters and nanometers are also used more frequently, but it becomes industry specific when actually doing things that small.
Valid, but rarely used, as it's usually just as fast to say "two hundred meters" instead of "two hecto meters".
However, those prefixes have other (non-SI) uses. A hectare is common way of referring to a 100x100 meter area. And a decare is 10 ares, i.e. 0.1 hectare.
I'd say we use every 3 prefixes, nanometerw, micrometers, mm, m, km, than any much higher than that usually uses space units (parsecs, AU, lightyears, etc.)
In The Netherlands we actually use “hectometerpaaltjes”, which translates to hectometer-signs. They are numbered signs placed on regional roads and highways every 100 meters, which is a hectometer. Although not a direct use of measurement, the term hectometer still is in active use this way.
As an American who has gotten very used to metric units in studying engineering, the general rule I picked up is that you typically only change units every three orders of magnitude. So 8 decameters would typically be expressed as 80 meters, maybe 0.08 kilometers. Decameters and hectometers are a thing, but they're not common units. Even centimeters don't see much use compared to millimeters.
We usually go for the 3 order rule, but in the case of areas and volumes, for dimensional reasons, dam and hm make it into the three order rule. Dm (or dam) is not common but dam^3 has some uses, the same goes for hm, hm is used for only special situations (like meassuring train distances), but hm^2 is almost globally used for big chunks of land. Also, with hm^2, we always keep the unit, so for example, Parque Nacional Iguazú in Argentina has 67620 hm^2 (also ha or hectarea).
I'm also an engineer and I generally despise imperial units, but I have to say that inchs are pretty handy and the 1 in = 25,4000... mm relation is pretty neat
From my experience in Norway, these are typical in context of daily speech:
Weight (gram): tonne (a substitute name for Mg (Mega)), kg, hg, g, mg, μg (mostly in medicine)
Distance (meter): mil (10 km), km, m, dm (kinda rare), cm, mm
Volume (liter): l, dl, cl, ml
In my experience, the deca-predix is very rarely used. Most of the missing prefixes are just substituted for numbers, i.e. saying "a thousand kilometers" is much more common that "a megameter". Of course, this differs depending on context, as a lot of the prefixes become more common within scientific fields where the sizes are common.
On a separate note, even the numbers can be a bit inconsistent. It has bothered me that it's often common to say "a thousand milliard" instead of "one billion" (also note that we use the long scale).
It depends on the situation, sometimes they are really handy but most of the time we stick to kilo, centi and mili.
Where i live, Hecto (100x) is used, for example to measure distances and areas for big properties. 1 hectometro equalls 100 m, or 1 hectarea (hm^2) equals 10000 m^2.
Also, it is widely use for pressure, cause 1 atm is 1013 hPa
Decameters are used but for special situations, like quantifying natural gas consumption
In Poland: decimeters are sometimes used (I have been ordering cut sheet metal priced by square decimeters) , I have not seen decameters in use. Hectopascales are often used in weather reports. Decagrams are often used when buying food where these amounts make most sense (meat, candy).
The 'more exotic' prefixes are usually only used with some specific SI units and in very specific contexts.
In Italy we use hectograms ("ettogrammi", "etti" for short) in day to day life when buying groceries. You don't ask for 200 grams of ham, you just ask for 2 etti.
We use litres, which is one decimetre cubed. We use hectares, which is one hectometre squared. But the beauty of it is, that you can just convert everything to units that are more widely understood.
Hektoliter is common in Germany for measuring quantities of beer (not a single serving, of course, but when buying beer for some kind of venue or measuring the output of a brewery)
In metric units, we primarily use the x1000 or x1/1000 steps, with a few notable exceptions. We use the centimeter (1cm = 1/100m) quite commonly, the centiliter (1cl = 1/100l) is also relatively common with drinks, and, IIRC, the Austrians use the deka, short for decagram (1dg = 10g).
I'm American, but follow mostly Europeans and Canadians online and use metrics in my own head just because it makes more sense.
I gather that the deca-/deka- and hecto- (along with a few other) prefixes are similar to imperial furlongs, leagues, stones, barrels, kegs, and hogsheads: They exist, but no one uses them outside of very specialized circumstances.
These two specifically - I don't think I've ever seen them.
Hectoliters are sometimes used e.g. for measuring beer consumption for an event, decimeters in some informal contexts, some country commonly describe drink sizes in centiliters or deciliters.
Centimeters are common, I'd say more common than millimeters in informal context.
I've seen some obscure uses in technical areas, but in general use no they aren't used. Metric is better skipping all those and using the thousands prefixes. cm is used but mm is much better. Europe uses cl but we in Canada don't, we use ml.
Europe uses cl, ml and dl. A can of coca Cola is 33 ml, a shot is 2 cl. Then you switch to litres at 0.5l.
We also use decilitre, but only in cooking, and I think most don't think of it as 0.1 l, but rather just think of it as the size of a measuring cup, i.e. it has more in common with "1 cup of sugar" than with "0.5 liter of water" in terms of how you think about it. More abstract, if that makes sense.
I used to do land surveying in Canada and we'd use "decs" for decimetres when laying out points. You'd put down the rod, they'd tell you something like "dec and a half left" then you'd move closer and it'd be "two cents right" and you'd be even closer and then it's like "3 mils right." Then you'd take the shot and they'd tell you how much closer or farther you'd have to go to get the point. If you were way off to the point where you might have tens of metres, usually for rough layout we'd rarely use "dee-kays" for dekameters, but typically it would be just "30 metres north".
Dekametre and hectometre, rarely. Mostly mm, cm, m, km.
In Europe, hg is relatively common, whereas in Canada, prices for deli products are "per 100 g" instead of per hg.
Also in Europe, cl and dl are common in recipes and bottles of alcohol, but in Canada, almost uniquely mL and L. (And yes, lowercase litre in Europe, but uppercase Litre in Canada, although that's gradually changing.)
German with a scientific background. I can deduce the meaning of the words but I've never seen them used. I'm not even sure these units of measurement were mentioned when these were discussed. Most stuff is ton, kilogram, gram, miligram, microgram; kilometer, meter, centimeter, milimeter, micrometer. Rarely decimeter are thrown around.