One sentence, five systems
The sentence is ฉันอยากเรียนภาษาไทย, “I want to learn Thai”. It has a high-class syllable with a rising tone (ฉัน), a silent อ that changes the tone of ยาก, a diphthong (เรียน), a long vowel in ภา, and the name of the language itself.
| System | ฉันอยากเรียนภาษาไทย | เชียงใหม่ (Chiang Mai) | Tones | Length |
|---|---|---|---|---|
| RTGS | chan yak rian phasa thai | Chiang Mai | no | no |
| IPA | /tɕʰǎn jàːk rīan pʰāːsǎː tʰāj/ | /tɕʰīaŋ màj/ | yes | yes |
| Paiboon | chǎn yàak riian paa-sǎa tai | chiiang-mài | yes | yes |
| Haas / AUA | chǎn yàak rian phaasǎa thay | chiaŋ mày | yes | yes |
| ISO 11940 | c̄hạn xyāk erīyn p̣hās̛̄ā ịthy | echīyngıh̄m̀ | written marks only | as spelled |
The ISO line has spaces between the words to make it easier to compare; the standard itself writes the Thai string letter for letter, and Thai has no spaces inside a phrase.
What each system is for
| System | What it is | Where you meet it |
|---|---|---|
| RTGS | Official transcription of the Royal Institute (now the Royal Society of Thailand) | road signs, maps, government documents, names of places |
| IPA | International Phonetic Alphabet | linguistics, dictionaries, precise descriptions of sound |
| Paiboon | Learner transcription from the Paiboon Publishing books | phrasebooks, learner courses, many online lessons |
| Haas / AUA | Mary Haas’s phonemic transcription, used in her dictionary and in AUA course books | older textbooks, linguistics, the AUA courses |
| ISO 11940 | International standard for transliteration: letter by letter, with diacritics | libraries, catalogues, round trips back to Thai script |
RTGS
The Royal Thai General System of Transcription is the official one, revised most recently in 1999. It uses only plain Latin letters, so it can go on any sign or form, and it writes the sound of a word rather than its spelling. The price is that it marks neither tone nor vowel length, and it writes several sounds the same way: ch for both จ and ช, o for four different vowels. ข้าว (rice), ข่าว (news) and ขาว (white) are all khao. It is the right system for finding a place on a map and the wrong one for learning to say a word.
IPA
The International Phonetic Alphabet has a symbol for every sound and marks tone with accents on the vowel: a macron for mid, a grave for low, a circumflex for falling, an acute for high and a caron for rising, with a length mark (ː) for long vowels. It separates the unaspirated p of ป from the aspirated pʰ of พ, and writes the Thai ch sounds as tɕ and tɕʰ. It is exact but unfamiliar, and Thai specialists differ on small points, such as how to write the diphthongs.
Paiboon
The system in the Paiboon Publishing books, and in many phrasebooks and online lessons, is built for English speakers. It doubles long vowels, marks tones with the same accents as IPA (leaving mid unmarked), and writes the unaspirated stops as bp, dt and g, so that ป, ต and ก cannot be mistaken for พ, ท and ค. It uses a few special letters for vowels English lacks.
Haas and AUA
Mary Haas, an American linguist, designed a phonemic transcription for her Thai-English Student’s Dictionary (1964). It is close to IPA but easier to type: c for จ, ch for ฉ and ช, y and w for the glides, ŋ for ng, doubled long vowels and tone accents. The AUA language centre’s course books use a version of it, and so do many older textbooks.
ISO 11940
ISO 11940 is a transliteration: each Thai letter has its own Latin form, with diacritics to tell apart letters that sound the same (a macron marks high-class letters, so ข is k̄h and ค is kh). Written tone marks are kept as accents, and vowels written before the consonant stay in front, so เรียน starts with e. The result tells you exactly how a word is spelled and almost nothing about how it sounds. Libraries and catalogues use it, or the similar ALA-LC system, because a reader can rebuild the Thai spelling from it. ISO 11940-2 is a separate, simplified transcription close to RTGS.
Why no system is “correct”
Each system answers a different question. RTGS asks what a Thai reader would accept on a road sign; IPA asks what a phonetician hears; Paiboon asks what an English speaker can read aloud without training; ISO asks how to get the Thai letters back. A system that does one of those well does the others badly. Even among the sound-based systems there are honest disagreements: whether to write ก as k or g, whether the vowel of ไทย ends in i, y or j, whether the high tone in modern Bangkok speech should be written as high or as rising.
The practical answer is to treat every romanisation as a temporary aid. Thai spelling, once you can read it, records consonant class, vowel length and tone marks, which together give the tone. That is more than any romanisation in common use, and it is the same in every book.
Romanisation on this site
The alphabet and anthem pages use RTGS, because it is official and is what you will see in Thailand. Where the tone matters, the guides add a learner’s transcription that doubles long vowels and marks tones with accents (à low, â falling, á high, ǎ rising, no mark for mid), and IPA where precision matters. The alphabet gives both RTGS and IPA for every consonant.