The various English dictionaries use different and sometimes conflicting IPA transcriptions for English. For example, the transcription /i/ may be used for the vowel of sit, of seat, or at the end of city. A dictionary may not even be consistent between one edition and the next. This table correlates the more widely used dictionaries with the conventions of the WP:IPA for English key that is used on Wikipedia.
Most dictionaries transcribe a specific dialect or accent, such as the Received Pronunciation (RP) of the Oxford English Dictionary, or a narrow range of dialects. Wikipedia's WP:IPA for English key, on the other hand, is intended to cover both RP and General American. As such, Wikipedia transcribes /r/ where it is found in rhotic dialects, but also the vowel distinctions found in non-rhotic dialects, without separating distinct UK and US pronunciations. Specific dialects may also be transcribed—local pronunciations of place names are often useful, for example—but they are normally written in addition to a more universal pronunciation.
When entering IPA in an article, please use the {{IPA}} template so that it is formatted properly on all web browsers. /Slashes/ and [brackets] should be included inside the IPA template, so that they display in the same font as the IPA itself. Also, please use proper stress ˈ and length ː marks (available at the bottom of your edit window) rather than the non-IPA shortcuts of apostrophe ' and colon :. Depending on the reader's font preferences, the latter can be ambiguous.
For a list of those languages other than English which have agreed-upon transcriptions in Wikipedia, see {{IPAhelp}}. For a comparison of the non-IPA transcriptions found in many US dictionaries, see Pronunciation respelling for English.
Consonants
Consonants vary little between dictionaries. The ones which do are those which start rich, /r ~ ɹ ~ ɻ ~ (r) ~ (ɹ)/; which, /ʍ ~ hw ~ (h)w ~ w/; and new, /njuː ~ nuː/. Wikipedia editors have decided to go with /ˈrɪtʃ/, /ˈhwɪtʃ/, /njuː/ for these words.
Vowels
Stress
One-syllable words may have stress. Most dictionaries leave it out, but that can be confusing when several such words are strung together. For example, in the name Zack de la Rocha, Zack and Rocha have stress, but de la does not. It would therefore convey an incorrect pronunciation to leave the stress mark off Zack: /ˈzæk dɛlə ˈroʊtʃə/.
Dictionaries also disagree on secondary stress. Generally, any stressed syllable prior to the last is marked as secondary (/ˌzæk dɛlə ˈroʊtʃə/), and that convention is followed here. However, several dictionaries also mark full (unreduced) vowels as having secondary stress when they come after the primary stress, even though they are not actually stressed. This practice is avoided on Wikipedia; if you have a word transcribed /ˈCVˌCV/, it should probably be /ˈCVCV/.