Definition: An abbreviation is a shortened form of a word. There are different kinds of abbreviations. Some use periods; others don't. Some are written in capital letters; others use lowercase letters. This is an area that is changing rapidly. It is always best to check a dictionary or a style manual to be certain.
People's Names and Titles
Abbreviations in people's names and titles generally do use periods, but academic degrees and Roman numerals do not require periods.
| Periods | |
|---|---|
| People's Names | People's Titles |
|
John Q. Adams (Quincy) S. E. Hinton (Susan Eloise Hinton) (Also notice that there is a space after the first initial in the second example.) |
Mr. (Mister) Mrs. (Missus, short for Mistress) Dr. (Doctor) Jr. (Junior) Sr. (Senior) |
| No Periods | |
|
Roman Numerals (after names of people or events) |
Academic Degrees |
|
John Parker III (pronounced John Parker the third, not John Parker three) World War II |
BA (Bachelor of Arts) MA (Master of Arts) PhD (Doctor of Philosophy) RN (Registered Nurse) |
Days and Months, Latin Phrases, Addresses Directions, and Traditional State vs. Postal State Abbreviations
| Periods | ||||
|---|---|---|---|---|
| Months | Days of the Week: Abbreviations of Three Letters or More | Addresses | Latin Phrases |
Traditional State Abbreviations (not frequently used anymore) |
| Jan. (January) |
Mon. (Monday) Tues. (Tuesday) Thurs. (Thursday) |
Ave. (Avenue) St. (Street) |
i.e. (id est = in other words) e.g. (exempli gratia = for example) etc. (et cetera = and so forth) |
Fla. (Florida) Mont. (Montana) |
| No Periods | ||||
| Days of the Week: Two- or Three-Letter Abbreviations |
Directions (all caps) |
US Postal Abbreviations (all caps) |
||
| Tu or Tue (Tuesday) |
NW (northwest) SE (southeast) |
FL (Florida) MT (Montana) |
||
Note: Three-letter abbreviations for days of the week can be written with or without a period at the end. Whether you decide to use periods or not, just remember to be consistent in your writing.
Tue. and Wed.
Tue and Wed
Measurements
Most measurements and scientific abbreviations do not use periods, but standard United States measurements and time abbreviations have a period at the end.
| Periods | |
|---|---|
| Standard US Measurements | Time Abbreviations |
|
in. (inch) ft. (foot) oz. (ounce)(The z in oz. comes from the Medieval Italian word onza.) |
sec. (second) h. or hr. (hour) |
| No Periods | ||
|---|---|---|
| Metric Measurements | Math and Science | Computer and Internet |
|
ml (milliliter) km (kilometer) cg (centigram) |
mph (miles per hour) mpg (miles per gallon) rpm (revolutions per minute) |
CPU (central processing unit) URL (uniform resource locator) DVD (digital video disc) |
Abbreviations in All Capitals
Abbreviations made up of the first letter of each word in a phrase, usually in all capitals, do not generally use periods, with some exceptions here and there.
|
Periods (Exception to the Above Rule) |
|
|---|---|
| The Abbreviation for District of Columbia | |
|
Washington, D.C. (D.C. has periods even though it is pronounced letter by letter.) |
|
|
No Periods (The Norm) |
|
| Acronyms | Abbreviations Pronounced Letter by Letter |
|
These are abbreviations pronounced as words instead of a string of letters. Some acronym abbreviations have actually become words themselves. NASA (National Aeronautics and Space Administration) NATO (North Atlantic Treaty Organization) |
FBI (Federal Bureau of Investigation) FYI (for your information) MVP (most valuable player) |
Abbreviations that Can Go Either Way
Some abbreviations are rapidly changing. Either form is generally accepted, but check with your teacher or style manual to make sure.
| Acceptable With or Without Periods |
|---|
| U.S.A. or USA |
|
B.C., A.D., C.E., B.C.E. or BC, AD, CE, BCE (B.C. or BC: Before Christ; A.D. or AD: Anno Domini; C.E. or CE: Common Era; B.C.E. or BCE: Before Common Era) |
|
a.m., p.m. or AM, PM If lowercase, use periods. If capitals, do not use periods. (a.m. or AM: ante meridiem/before midday; p.m. or PM: post meridiem/after midday) |
Abbreviations and End Punctuation
If you end a sentence with an abbreviation containing a period, do not put another period at the end of the sentence. However, if a sentence ends in an exclamation mark or a question mark, include both the abbreviation's period and the end mark.
His son's name is Jason Miller Jr. (abbreviation period only, no end period)
Is his son's name Jason Miller Jr.? (abbreviation period + ending question mark)