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Capitalizing Unit Abbreviations

Date: 09/15/2003 at 12:11:38
From: Ricky
Subject: Metric Measurement

Why do we use a lowercase m to abbreviate meters, but an uppercase L
to abbreviate liters? 

Actually, I've always seen both used either way.  Which is right?  Or
are they both right?

Date: 09/15/2003 at 15:22:54
From: Doctor Peterson
Subject: Re: Metric Measurement

Hi, Ricky.

The m is always lower case, but the L may be either. See this page: 

  liter or litre (L or l) 
  the common metric unit of volume. ... Both the lower case letter l
  and the upper case L are accepted as symbols for the liter, but
  the U.S. Department of Commerce specifies that L be used, at least
  by businesses, to avoid confusion with the numeral 1. The unit is
  spelled liter in the U.S. and litre in Britain; there are many
  other spellings in various languages (see Spelling of Metric

This page gives the general rule: 

  Units: The names of all units start with a lower case letter
  except, of course, at the beginning of the sentence. There is one
  exception: in "degree Celsius" (symbol C) the unit "degree" is
  lower case but the modifier "Celsius" is capitalized. Thus, body
  temperature is written as 37 degrees Celsius.

  Symbols: Unit symbols are written in lower case letters except for
  liter and those units derived from the name of a person (m for
  meter, but W for watt, Pa for pascal, etc.).

  Prefixes: Symbols of prefixes that mean a million or more are
  capitalized and those less than a million are lower case (M for
  mega (millions), m for milli (thousandths)).

There is some variation in preference between countries: 

  The symbol for liter (or litre) may be either a capital el (L) or
  a lowercase el (l); both are correct. In the U.S., Canada, and
  Australia, the capital el (L) is preferred, but most other nations
  use the lowercase el (l).

This gives a nice explanation for Liter: 

  Please Note: Where symbols are used convention has it that they
  are always lower case letters except where the Base Unit is named
  after a person like Celsius (C), Pascal (P) or Newton (N). Then
  the symbol is noted by a CAPITAL LETTER.
  So what's with a capital letter "L" for liter?
  Is that a capital "L" for the unit of measure named after a person?
  You see, when decimal dimensions were described long before the
  typewriter you would have to write the script "l".
  But as technology came along it became apparent that typewriters
  were not equipped with the script "l" so attempts were made to use
  the lower case "l" (el).
  Then it became further confusing to write "1l" (lower case "el")
  as the "1" and "l" (el) looked too similar as did the capital "I"
  So the capital "L" was chosen as the symbol for the derived base
  unit "liter". 

If you have any further questions, feel free to write back.

- Doctor Peterson, The Math Forum 
Associated Topics:
Elementary Terms & Units of Measurement
Middle School Terms/Units of Measurement

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