The Liter is Not All Wet


By The Metric Maven

Bulldog Edition

My friend Pierre spends a lot of time browsing for backpacks and such. I suspect he has always wanted to runaway from home, but just never has found exactly the right luggage. One day he came across a backpack with a capacity of 1700 cubic inches or 28.7 liters. This caused him to think about a new unit which is appropriate for storing Jimmy Hoffa or other expired homo sapiens. Pierre saw no reason that he should not suggest a new unit for SI because he had discovered how compromised the liter is:

“So for that one moment in time, I thought about how we communicate volume to others. Moving hand gestures seem to work, but that doesn’t help in print advertising. Usually, we use “cubic inches,” or “cubic feet.”

But, the French get wet. They use quarts/liters/litres/litrons and cubic decimetres for everything, apparently. …”

Then Pierre goes for the jugular:

“Speaking of which, liters aren’t actually an SI unit? I’ve been lied to? Maybe you should get on that with your foreign pals. Or just toss it and use quarts like everybody else does.

As an example, note this bag on sale on Amazon this week, specifically the part I highlighted en rouge:


Unlike an insanely hot, but, hairy-armpitted, chain-smoking French girl, we smartly measure volume by linear methods cubically applied. They just go right to liquids. How funny would it sound for us to say this bag could contain 108 cups of coffee (real cups, not “coffee cups”) . One could kind-of picture that. But saying “this bag holds 27,000,000 cubic millimeters?” Not so useful.

Even a mostly dim marketer can immediately see that metric isn’t good for advertising AT ALL.

Unless this is a “wet bag” of some sort, isn’t the metric system inappropriate here?

Who uses wet measurements to measure dry things? Besides luggage and motorcycle/car engine manufacturers. Those goose-feeding, croissant-eating French, that’s who. Well, and baking measurements too. But that’s just wrong.”


The good news is that Pierre’s understated, quiescent and measured questioning provides me with an excuse to explain the importance of the liter—otherwise known as the Rodney Dangerfield of the metric system. First one must realize that wet and dry volumes are equivalent, and no distinction is necessary. In cooking, wet measurement cups have a line below the top, and are generally clear. Dry measures are made so that the exact measure is at the rim of the cup. One can scrape them flat with a knife and have the exact same volume as the wet value, but in a way that works better for dry stuff. It was Isaac Newton who changed cooking forever by defining mass. After that point, much like the metric system, the English creation was adopted by the French. They realized that dry ingredients were best weighted in the Earth’s gravitational field, which allows one to back out the mass in grams. I think we know what happened to English versus French cooking at that point.

There is no distinction between wet and dry volume in reality; but in the imagination of English speaking people, somehow a magical change occurs. Exhibit A is the US Gallon (Wikipedia):

The US liquid gallon

The US gallon, which is equal to approximately 3.785 litres, is legally defined as 231 cubic inches.[1][2] A US liquid gallon of water weighs about 8.34 pounds or 3.78 kilograms at 62 °F (17 °C), making it about 16.6% lighter than the imperial gallon. There are four quarts in a gallon, two pints in a quart and 16 fluid ounces in a US pint, which makes a US gallon equal to 128 fl. oz. In order to overcome the effects of expansion and contraction with temperature when using a gallon to specify a quantity of material for purposes of trade, it is common to define the temperature at which the material will occupy the specified volume. For example, the volume of petroleum products[3] and alcoholic beverages[4] are both referenced to 60 °F (16 °C) in government regulations.

The US dry gallon

This gallon is one-eighth of a US Winchester bushel of 2150.42 cubic inches; it is therefore equal to exactly 268.8025 cubic inches or 4.40488377086 L. The US dry gallon is not used in commerce, and is not listed in the relevant statute, which jumps from the dry quart to the peck.[5]

The liter is fixed in value. It is a 100 mm x 100 mm x 100 mm cube. The gallon?—-not so much.

The liter was clearly designed by Father Nature (wait till Mother Nature finds out) as it is a cube with edges which are very close to the width of an average man’s hand. This allows an average man to estimate a liter of volume very quickly.

SI, in its semi-infinite wisdom, made the cubic meter the official unit of volume, and the liter was relegated to second class citizen status. When the Australians decided to become a metric nation, they were apparently far enough away from the bad influences of the US, Canada and the UK to realize (from Metrication in Australia):

Metrication In Australia

Yes, even applications that involve describing the volume of a backpack. The backpack could be described as 28 700 milliliters (or 28 700 – 10 mm cubes), but any person slightly acquainted with the metric system will immediately see 28.7 liters, and would not understand the importance of extra numbers for marketing purposes. When actually attempting to present numbers in an understandable way, the liter is excellent. Water has a density of 1000 grams/L. If any SOLID object has a density higher than this it sinks, if it’s lower it floats. Wet and dry coexisting in harmony, without an artificial separation, because of the liter.

If you liked this essay and wish to support the work of The Metric Maven, please visit his Patreon Page and contribute. Also purchase his books about the metric system:

The first book is titled: Our Crumbling Invisible Infrastructure. It is a succinct set of essays  that explain why the absence of the metric system in the US is detrimental to our personal heath and our economy. These essays are separately available for free on my website,  but the book has them all in one place in print. The book may be purchased from Amazon here.

The second book is titled The Dimensions of the Cosmos. It takes the metric prefixes from yotta to Yocto and uses each metric prefix to describe a metric world. The book has a considerable number of color images to compliment the prose. It has been receiving good reviews. I think would be a great reference for US science teachers. It has a considerable number of scientific factoids and anecdotes that I believe would be of considerable educational use. It is available from Amazon here.

The third book is called Death By A Thousand Cuts, A Secret History of the Metric System in The United States. This monograph explains how we have been unable to legally deal with weights and measures in the United States from George Washington, to our current day. This book is also available on Amazon here.

d this essay and wish to support the work of The Metric Maven, please visit his Patreon Page

16 thoughts on “The Liter is Not All Wet

  1. Or you could say is holds 0.0287m^3 or I can think of squishing 14 2l bottles of soda into the space?

    Seems to me that volume isn’t really the right information in the first place – I would find it much more useful to have approximate H x W x D.

    • I find that specifying capacity in litres for an appliance such as a refrigerator is useful as it allows me to visualise an array of one-litre milk cartons that would fill it.

      A quick look at the site of an Australian home goods vendor shows not just fridges, but freezers, ovens and microwave ovens all with volumes in litres. Washing machines and dryers have their capacity specified in kilograms.

      I also looked up backpacks on a camping goods store and found the volume capacity in litres, load capacity in kilograms but L x W x H in centimetres and inches.

    • or 28.7 dm³, since the liter is merely a special name for the cubic decimeter. Of course, the SI Brochure allows the decimeter and the metric Maven doesn’t.

  2. Maven: I started reading your current essay and suddenly stopped in your second sentence, saying to myself something like, “Oh, not again.”

    Here’s the sentence: “I suspect he has always wanted to runaway from home, but just never has found exactly the right luggage.”

    Why another “exactly”?? Not long ago I read that some surveys showed “whatever” to be the most annoying word for several consecutive years. Apparently the unnatural word “exactly” seems to have taken over.

    Unnatural word? Let’s put a natural word in the Maven’s sentence instead to make the point clearer: I suspect he has always wanted to runaway from home, but just never has found just the right luggage.

    Furthermore, in relation to SI, an actual measurement cannot be exact as such is of something continuous. Thus, we have the prefixes milli-, micro-, nano-, … , yocto- to give us the appropriate precision, not “exactness”.

    Guess I’ll get back to reading the Maven’s latest essay later…

  3. More good points maven! I think milk should be sold in liters, that would lay the ground work for change. Why, because the gallon of milk I grew up with is still the touchstone of thinking concerning volume comprehension.

    I just paid $189.00 for a gallon of gasoline, damn you Obama!

  4. Actually, nothing in the SI Brochure says the liter can’t be used for dry volumes.
    The SI declares that the word litre (liter in US English) is a special name for the cubic decimeter. In principle, it is no different from the status of the tonne or hectare; units which are not formally SI, but are permitted for use with the SI (Table 6).

    The only reason that the US has different size gallons is that the British, at the time of the Revolution and before, had three gallons, wine, ale and grain. Each had a bushel 8X larger. We apparently never adopted anything related to the ale gallon, but we adopted the wine gallon for liquids, and the bushel related to grain gallon for dry things. By 1824, after two wars with the British, we adopted nothing from the changes in the Imperial Act. Both the US gallon and bushel have legal definitions in cubic inches which may be converted to cubic decimeters or liters. Just multiply the cubic inches by (0.254 dm/in)³

  5. In a nutshell, the problem with the liter is it is not coherent. As such, it is just an alternative name for one cubic decimeter, or, as the deci-immune Maven would have it, one million cubic millimeters.

    The Maven’s guidelines are clear with respect to the noncoherent liter: The only prefixes that should be used with it are milli- and micro-.

    Also, as Em indicated, selling milk by the liter in the U.S. would be groundbreaking, something I believe the USMA has been advocating for a great many years sans success.

    Will such a day come? It should, especially since the difference between a quart and a liter is only about 55 mL, and so little is lost, or in this case, gained. (Of course the big problem is with those innumerate anti-metric “progressives”, many of whom go by the appellation “teacher”…)

  6. David B et al., for the most irritating word in modern English, I nominate “awesome.” When, during his famous 1968 “I shall not seek” speech, the late President Lyndon Johnson referred to the “awesome duties” of the Presidency, I sympathized. His world choice was appropriate for the subject. But today, so many facts and pleasures are described with that word that my eyes glaze over continually. I wish, for a time, to change it back to a word of my youth: “groovy!”

    Maven, as I was reading your description of the U.S. gallon, I remember an old attitude I had towards measurement, and I think it one that many Americans cling to. It’s the “that’s its realm, that’s the way it is.” It’s the idea that measurement has to be so complicated, because our attitude towards it has always been what I suppose we could call the “gallon attitude,” that it is defined as 231 cu. in., and a gallon of water exists best at 17 C. I suppose the latter data are necessary for commercial purposes, and gasoline volume has become an issue lately (I do note well that hydrogen fuel shall be sold by the kilogram. If we were to start doing that with gasoline, oy vay, so many changes in thought!).

    Thanks again, Maven, for a great column. You write some of the best material in metrication. There shall be a time when certain literature is considered for preservation in the Smithsonian Institute or by the National Archives and records Service, and just about all your columns beg for such preservation when this history of our country’s metrication is completed.

    • Paul:

      Wrt “awesome”, it’s the slang use of it that’s irritating; today, it seems “awesome” has now become “dope”, another slang word (like that of your youth, “groovy”).
      Wrt “exactly”, its overuse is not in any way slang but just plain wrong when the word should be “precisely” (which I recall from more youthful days; anyway, today exactly-vs-precisely usage is a good litmus test in assessing one’s level of education), or more generally “just”.
      Again, wrt SI, measurement is of things continuous, not discrete, and so there is little use for exactness and much use for precision…

  7. If the cubic meter regained its original name (or got another, new name), i.e. the stere (and let’s abbreviate it simply as S, here, for simplicity), one liter would simply be one millistere:

    1 L —> 1 mS

    … and thus that backpack would have a volume/capacity of 27.8 mS; and also no need for the decimeter to define the unit.

    Of course, the liter is a much more “customary” (sic!) or practical unit for everyday use, but in principle there would be no problem whatsoever in adopting the cubic meter as the unique base for volume: we would just need to “think bigger” (and the same could of course be said also for the tonne, as a mass unit)…

    • EuroCity and Others:

      In “adopting the cubic meter as the unique base for volume”? Such is already the unique base unit for volume, just like the square meter is the unique base unit for area. Why? Simply because the meter is the unique base unit for length!

      • Yes, but of course I meant that the cubic meter would just need a name, in order to be really usable also in everyday life: one cannot practically use milli-cubic meters, while there would be no problem in using millisteres, or whatever old or new name for the cubic meter (one could even redefine the liter to be one cubic meter).

        Instead of allowing a lot of additional “customary” units, wouldn’t it be better to improve the SI in a systematic way? IMHO, yes (even if sadly there are probably no plans to do that)…

        • The other option, if we don’t want to base additional pseudo-SI units on the decimeter or the centimeter, is to use cubic millimeters for “small” volumes; but that’s probably not so practical, after all: 27.8 liters would be 27 800 000 cubic millimeters – and you cannot concatenate prefixes.

          So, either we accept the decimeter (and centimeter) as full SI citizens (with the liter), or we find a name for the cubic meter and just use SI prefixes with that…

          • The decimeter and centimeter are full SI citizens whereas the liter is not.

            The SI Brochure makes explicit use of the centimeter, decimeter and hectometer in the (SI) definitions of the liter and hectare, which, along with the tonne, are “non-SI units accepted for use with the International System of Units.” (Table 6).

            • But the Maven – and others – doesn’t want decimeters and centimeters, while the liter is gladly accepted: which is rather a contradiction, isn’t it – being that the liter is based on the (cubic) decimeter…?

              The real advantage of the liter, OTOH, is – besides being of the “right” size for bottles, etc. etc. – that it has a practical, everyday name (instead of a non-prefixable “cubic-anything”)…

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