Claude Émile Jean-Baptiste Litre

An interesting and little-known story about the liter symbol

The preamble. There is a general rule: if a unit of measurement is named after a person, its symbol must be capitalized.

Example: there was once a lord Kelvin, named William Thomson. The unit of temperature measurement was named after him, kelvin. It is a common noun and must not be capitalized. But its symbol K is capitalized because the unit of measurement is named after a person. Writing k here is an error.

Surprisingly, the liter is not named after a person. This word is derived from an Old French unit of volume (litron), and that is why l is not capitalized.

In languages with non-Latin alphabets, this symbol doesn’t cause any problems. But the small Latin l and I (capitalized i) letters and the 1 number look too much alike. In some fonts, they are practically identical. It is very confusing.

To avoid confusion, instead of l, L began to be used for liter, even though it is prohibited by the SI system.

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And now the amble. To “legalize” the prohibited L symbol, one funny person invented a man named Claude Émile Jean-Baptiste Litre and his complete “biography,” which was published as an April Fool joke in a scientific journal. This Litre was allegedly a son of a wine bottle manufacturer and suggested a unit for measuring their volume. And since it is a person, the liter L symbol must be capitalized.

The joke was much appreciated, and there were even attempts to develop Litre’s biography: some members of the scientific community started inventing his sons and daughters. However, many respectable scientists failed to recognize the joke and began citing this article as a source. And they still do.

The case of Monsieur Litre has become so grand that in October 1979, at the 16^th General Conference on Weights and Measures, a resolution was approved that made an exception and legally allowed the use of both l and L as symbols for liter.

When buying a bottle, look closely: most likely, liter there will be mentioned as L.