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### Proper Abbreviation of Measurement Units

```Date: 03/04/2004 at 09:25:51
From: Norma
Subject: Customary measurement abbreviations

Is a period used after the abbreviations for the customary units of
measurement?  In the past, I understood that all abbreviations used a
period.  Now, I typically see inch as in., but ofter see foot (ft),
yard (yd), and others with no period.  I think maybe in. is used so as
not to be confused with the word "in".

```

```
Date: 03/04/2004 at 12:21:40
From: Doctor Peterson
Subject: Re: Customary measurement abbreviations

Hi, Norma.

As the following page points out, there is no "official" rule for
writing customary units, as there is for SI (which omits all periods
in unit symbols):

Using Abbreviations or Symbols
http://www.unc.edu/~rowlett/units/symbol.html

That site chooses to follow SI rules for all units, so that no periods
are used, even for "in".  I found various writing style guides that
recommend the rule you have observed, omitting the period except after
"in.", presumably because of potential confusion.  Here is one:

ASAE Authors' Guide
http://www.asae.org/pubs/style.html

Omit periods after abbreviated units (except "in." for inch):

5 m, 30 cm, 40 ft

This presumably results from familiarity with the metric system and
its rules, which then spread to other units for the sake of
consistency.  Whether "in." will lose its period in common usage
before the inch is fully replaced by the metric system is a good
question!

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

- Doctor Peterson, The Math Forum
http://mathforum.org/dr.math/
```
Associated Topics:
Elementary Terms & Units of Measurement
Middle School Terms/Units of Measurement

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