The end of every sentence must be marked with a full stop, question mark or exclamation mark.
Some people are unsure where a sentence ends and may mistakenly leave them out. For example, in this collection of words, there must be a full stop after news.
- He was astounded at the news he didn’t know what to say.
(For more on this, see Sentences and clauses.)
We also use full stops for certain abbreviations; for example:
- Smith and Co.
- Sometimes with a.m. and p.m.
- Sometimes with abbreviations of month names
Note that abbreviated scientific and metric units of measurement should never have a full stop (unless at the end of a sentence).
- ’The rectangle was 16cm by 22cm’ is correct.
- ’The car exceeded the speed limit of 50 km/h’ is correct.
However, where an abbreviation starts and ends with the correct letters of a word, then there is no stop; for example, Mr , Mrs , Ms and Dr and similar abbreviations.
Many well-known names or titles are not used with full stops and so we regularly see MP without any full stops as well as the USA, UK, UN, UNICEF and so on.
Accepted convention varies in different parts of the English-speaking world. In American English, full stops to separate the letters in an abbreviation are more likely to be used than in British English.
Although you will see variations in usage, you need to check what is acceptable within a particular environment or type of writing and above all be consistent within your own essay or other piece of writing.