Thai Romanization: Why “Sawasdee”, “Sawatdee” and “Sà-wàt-dii” All Exist

Thai words appear in many different Latin spellings because there is no single romanization that everyone uses. The official system, RTGS, is the one on road signs and maps, but it shows neither tones nor vowel length. Learner systems such as the one used on this site add accents for the tones and double the long vowels, and linguists use the IPA. “Sawasdee”, “sawatdee”, “sawatdi” and sà-wàt-dii are all attempts to write the same word: สวัสดี, “hello”.

Why are there so many ways to write Thai in English letters?

Thai has features that the Latin alphabet was never designed for: five tones, short and long vowels that change the meaning, vowels such as ʉ or ɔ that English does not have, and three different kinds of p (บ, ป and พ). Every romanization has to decide what to show and what to leave out, and different systems decide differently.

There is also a deeper split between two goals:

• Transliteration copies the letters. Thai spells “hello” with a ส (s) at the end of the second syllable, so a letter-by-letter spelling gives “sawas-”.
• Transcription writes the sound. That ส is pronounced t at the end of a syllable, so a sound-based spelling gives “sawat-”.

Add English spelling habits (“ee” for a long i) and you get the whole family:

RTGS: the official romanization

The Royal Thai General System of Transcription (RTGS) is published by the Royal Institute of Thailand; the current version dates from 1999. It is used for place names, maps, government documents and most road signs, and it is the system behind spellings like Krung Thep (Bangkok), Thong Lo or Phrom Phong on the BTS map.

RTGS was designed to be easy to type with plain Latin letters, so it leaves out a lot:

• No tones. Nothing in the spelling tells you whether a syllable rises, falls or stays flat.
• No vowel length. Short and long vowels are written the same way.
• Merged vowels. The two Thai o sounds (โ and อ) are both written o; แ is “ae”, the ʉ sound is “ue”, and the ə sound is “oe”.
• One spelling for two consonants. จ and ช are both written “ch”, although จ is unaspirated and ช is aspirated.

The result is that very different words can share one RTGS spelling:

“Near” and “far” look identical in RTGS. That is fine on a road sign, where you only need to recognise a name, but it is not enough to learn to speak.

Road signs also keep some older spellings that predate the system. The sign for Bangkok’s great avenue reads Sukhumvit, while strict RTGS would write Sukhumwit; the airport is Suvarnabhumi, a spelling based on the Sanskrit form of the name, while RTGS gives Suwannaphum and Thais say sù-wan-ná-puum.

Why “kh”, “th” and “ph” are not what they seem

In RTGS, an h after k, t or p means that the consonant is aspirated: pronounced with a small puff of air, like the k in “kin” or the p in “pin”. Without the h, it is unaspirated, like the k in “skin” or the p in “spin”. It never stands for the English th of “think” or the ph of “phone”.

So the th of Thailand is simply the t of “tie”, Thong Lo is tɔɔng-lɔ̀ɔ, and Phuket is puu-gèt, with no f anywhere.

The system on this site writes the same contrast from the other side. It keeps k, t, p for the aspirated sounds and uses g, dt, bp for the unaspirated ones:

The unaspirated ต sits between an English d and t, and ป between b and p: “dt” and “bp” are reminders of that in-between sound, not two letters to pronounce one after the other. Once you know the convention, ขอบคุณ is kɔ̀ɔp-kun here and “khop khun” in RTGS: the same word, the same sounds.

Tone-marked systems for learners

Learner books and apps need what RTGS leaves out, so most of them use their own system. The transliteration on this site is Paiboon-style, the kind popularised by the Paiboon Publishing textbooks:

• tones are accents on the vowel: mid has none (maa), low a grave (jàak), falling a circumflex (mâi), high an acute (kráp) and rising a caron (pǒm);
• long vowels are doubled (dii, sǔun), short ones are single (jèt);
• vowels missing from English get their own symbols: ʉ (chʉ̂ʉ), ɔ (kɔ̀ɔp-kun), ɛ (mɛɛo), ə (dəən);
• the syllables of one word are joined by hyphens (sà-wàt-dii).

Other textbooks use other conventions, such as “aw” for ɔ or tone numbers after each syllable. None is wrong; what matters is that a system shows tones and length, and that you stick to one. The transliteration key in our alphabet guide sums up every symbol.

IPA: the linguists’ standard

The International Phonetic Alphabet is the most precise option. It marks aspiration with a raised h (kʰ), length with a colon-like sign (aː) and tones with accents or tone letters. Dictionaries and linguistics books use it, but its symbols (tɕʰ for ช, ŋ for ง) make it heavy for everyday study. It is worth recognising, especially when you check a pronunciation online.

Common Thai words in RTGS, this site’s system and IPA

Two details stand out. RTGS “pla” and this site’s bplaa describe the same unaspirated p, written from opposite conventions. And the menu spelling “pad thai” is neither system: its d copies the letter ด, which is pronounced t at the end of a syllable.

Why do Thai people romanize Thai in different ways?

Visitors are often surprised that Thais themselves spell their own words in many ways. The reason is simple: Thais learn to read in Thai script and do not need romanization for their own language. It is used mostly for foreigners and for official documents, and outside place names nobody enforces a standard.

• Personal names are romanized freely for passports and business cards, often letter by letter, including letters that are silent in speech. Two people with the same Thai name can spell it differently in English.
• Brands, menus and shop signs follow habit and English spelling: “ee” for ii, “oo” for uu, “pad” for ผัด.
• Old and new spellings live side by side, like Siam and the RTGS form Sayam for สยาม (sà-yǎam), the name of the BTS station Hugo struggles to get out of in The skytrain.

How to use romanization without getting stuck

1. Pick one system with tones and stick to it. Mixing a phrasebook, a video and a menu means three spellings for every word.
2. Never guess the pronunciation from a sign. Treat RTGS spellings as names to recognise, not as instructions for your mouth.
3. Use transliteration as a bridge, not a destination. Thai script is the only spelling that is the same in every book, on every sign and in every text message, and it encodes the tones. Our guide on how to read Thai shows how to start.
4. Learn the script with words you already know. Kru May shows every word in Thai script with its transliteration and audio, so you can read stories from the first day and lean on the romanization less and less. Reading with audio is the core of our approach to learning Thai with stories.