Use a hyphen (-) to make compound words. You can also use them to link prefixes or suffixes to the word they modify (always check the dictionary and word list).
Do not put a space on either side of the hyphen.
As a general rule, don't link prefixes (un-, multi-, post-) or suffixes (-ism, -ify) with a hyphen unless you can improve clarity with its inclusion. Readers will find co-worker much easier to read than coworker. However, cooperate doesn't present the same issue.
• Prefix: co-branding
• Two-word phrasal adjective: list-formatted line item, hard-coded string
• Three-word phrasal adjective: off-balance-sheet accounting
Note that if the phrasal adjective follows the noun, you don't need the hyphen (a well-known software company but that software company is well known). However, some fixed phrases such as cost-effective and old-fashioned are always hyphenated. Check the AP Style Guide for more nuanced guidance and Merriam-Webster(opens external page) for other examples of fixed phrases.
Use a hyphen between numerals and units of measurementif the unit of measurement is not abbreviated (52-inch screen). However, if an abbreviation for the unit of measurement is present, discard the hyphen (You need 20 GB of free space).
A hyphen is not needed with very or with adverbs that end in -ly (recently saved model).
very large data set
expertly constructed calculation
mostly ASCII characters
very-large data set
Suspended hyphens, also called suspensive hyphens, replace repeated words, prefixes, or suffixes in two or more compound modifiers (short- and long-term planning, first-, second-, and third-level models).
Be careful with this usage, especially in technical content (and avoid whenever possible in interface copy). Consider your reader's literacy level and be mindful of adding complexity for translation. If in doubt, try to write the sentence in a simpler way.
Keyboard shortcuts / keyboard keys
When writing keyboard shortcuts using combination keystrokes, do not use hyphens to signify that the first key or keys should be held down while the last key is pressed. Use the plus sign (+) instead. (Don’t use the plus sign if each key should be pressed and released separately.)
Prefixes that require hyphens
co-worker (but: cooperate, coordinate)
Prefixes that do not require hyphens
web-site (or web site)
Common compound words that require hyphens
|medium-size (never sized)
|to indicate location
|lower-left corner, upper-right side of the screen