Abbreviations: make the first mention clear

An abbreviation saves space only when the reader understands it. Give the full form at first mention when the audience may not know it.

Use the pattern in context

A useful pattern is full name followed by the short form in parentheses: estimated time of arrival (ETA). Then use the short form consistently. Some shortenings are read as letters, such as PDF; others are spoken as words. The sound, not the first written letter, controls a or an: a PDF, an ETA.

Examples to compare

First mention: estimated time of arrival (ETA).
Request: Could you send the file as a PDF?
Clarify: What does that abbreviation stand for?

Limits and useful distinctions

An abbreviation may mean different things in different fields. Spell it out in an unfamiliar or important message rather than guessing. Styles differ over full stops and capitalization, so follow the document’s style. This is a small communication guide, not a universal directory of initials.

Check your understanding

Would you write a ETA or an ETA when speaking the letter names?

Reveal the answer and reason

An ETA.

The spoken letter E begins with a vowel sound. Read the guide

Try a new example with the same purpose. Check that your version keeps the intended meaning and grammatical pattern.