Note: If you don't know the difference between transliteration and transcription I suggest that you read these notes first: Transliteration vs. Transcription. You'll probably find you don't need to read these notes. For everyone else, you probably don't need to read these notes either.

Google Translate provides transliteration of Thai text when translating from Thai to another language. However, there appears to be no public description of how that transliteration works. These notes try to plug that deficiency.

The following table shows how Thai characters are transliterated by Google Translate

Notes

1. Where consonants have the same sound in initial position, the transliteration uses the same consonant for each Thai letter, adding diacritics to distinguish them, e.g. ซ/ศ/ษ/ส are transliterated as s/ṣ̄/s̄ʹ/s̄.
2. For the unaspirated/aspirated consonant pairs (ก/ค จ/ช ป/พ ต/ท) the aspirated consonants are represented by digraphs with the second character h representing aspiration e.g. k/kh c/ch.
3. ง and ๚ are also represented by digraphs - ng and ||.
4. For short/long vowel pairs the long vowel has a macron, e.g. ◌ุ/◌ู is transliterated u/ū.
5. Leading vowels (เ, แ, โ, ใ, ไ) are written after the initial consonant so, for example, ไทย is transliterated thịy and โลก is lok. However, where a word starts with a consonant cluster, the leading vowel is written after the first consonant - not the consonant cluster, e.g. แปรง is pærng and ไทร is thịr
6. Unwritten vowels such as o in บน and a in สบาย are also not written in the transliteration - bn and s̄bāy.
7. Tone marks and other above symbols are written as diacritics above the vowel.
8. Google Translate capitalises the first consonant of every phrase.