Phonemic vs Phonetic Transcription
A question that comes up a lot in pronunciation teaching is about the difference between two ways of transcribing sound: phonemic and phonetic:
Quiz (5 questions)
Slants, Bars, Brackets & Square Brackets,
Phonemic transcriptions are normally made with slants //, but some dictionaries use standard brackets ( ) and others use bars | |.
Phonetic transcriptions only use square brackets [ ].
The Phonemic Alphabet
A phonemic alphabet has a basic principle: 1 symbol = 1 sound. This means that in a word such as PARK, there are 3 phonemes in British English /pɑːk/ and 4 phonemes in American English /pɑrk/.
General British English is generally understood to contain 44 phonemes, as shown on the phonemic chart below:

A strict phonemic transcription can only use the symbols on a phonemic chart.
The Phonetic Alphabet
A phonetic alphabet is much broader. The International Phonetic Association releases the most commonly used phonetic alphabet, which you can see below:

You can see that the range of symbols is much greater with many options to modify sounds using additional symbols or diacritics.
This is the huge advantage to phonetic transcription – you can describe what is being said with much more precision:

But this also poses a problem: how much detail should we include?
The lack of limits can be confusing for teachers and learners of English.
However, it’s worth remembering that phonetic transcription has multiple uses ranging from speech pathology to linguistic fieldwork, so the vast options are useful in many contexts.
Details, Accents & Variations
The key advantage that phonetic transcriptions give learners of English as a second language, is access to the nuances of pronunciation that phonemic alphabets cannot show.
Key details such as aspiration, glottal stops, pre-fortis clipping and sounds in free variation, can be shown with a phonetic transcription.
This is also true for those studying regional accents of English – a phonetic transcription can show the different vowel positions and subtle changes in consonant production.
Some examples are found below (see the video for audio) where the last column is transcribed in a regional accent of Britain:

Both phonemic and phonetic transcriptions have their advantages. For learners who are new to pronunciation, phonemics is the place to start, but for those who aim for a more thorough and advanced understanding of English pronunciation or accents, embracing the phonetic chart is essential.