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There are 44 consonants representing 21 distinct consonant sounds. Duplicate consonants represent different Sanskrit and Pali consonants pronounced identically in Thai (although the distinction between the consonants is retained in spoken Khmer). The consonants are divided into three classes - low (siang tam เสียงต่ำ), middle (siang klang เสียงกลาง) and high (siang sung เสียงสูง) - which determine the tone of the following vowel. There are in addition four consonant-vowel combination characters not included in the tally of 44.
To aid learning, each consonant is traditionally associated with a Thai word that either starts with the same sound, or features it prominently. For example, the name of the letter ข is kho khai (ข ไข่), in which kho is the sound it represents, and khai (ไข่) is a word which starts with the same sound and means "egg".
Two of the consonants, ฃ (kho khuat) and ฅ (kho khon), are not used in written Thai anymore. Some say  that when the first Thai typewriter was developed by Edwin Hunter McFarland in 1892, there was simply no space for all characters, thus two had to be left out. Also, neither of these two letters correspond to a Sanskrit or Pali letter, and each of them, being a modified form of the letter that precedes it (compare ข and ค), has the same pronunciation and the same consonant class as the preceding letter. This makes them redundant.
Equivalents for romanisation are shown in the table below. Many consonants are pronounced differently at the beginning and at the end of a syllable. The entries in columns initial and final indicate the pronunciation for that consonant in the corresponding positions in a syllable. Where the entry is "-", the consonant may not be used to close a syllable. Where a combination of consonants ends a written syllable, only the first is pronounced; possible closing consonant sounds are limited to 'k', 'm', 'n', 'ng', 'p' and 't'.
Although an official standard for romanisation is defined by the Royal Thai Institute, many publications use different Romanisation systems. In daily practice, a bewildering variety of Romanisations are used, making it difficult to know how to pronounce a word, or to judge if two words (e.g. on a map and a street sign) are actually the same. For more precise information, an equivalent from the International Phonetic Alphabet (IPA) is given as well.
Each consonant is assigned to a "class" (Low, Middle, High), which plays a role in determining the tone with which the syllable is pronounced.
|ก||ko kai (chicken)||k||k||k||k||M||ก|
|ข||kho khai (egg)||kh||k||kʰ||k||H||ข|
|ฃ||kho khuat (bottle) [obs]||kh||k||kʰ||k||H||ข|
|ค||kho khwai (water buffalo)||kh||k||kʰ||k||L||ค|
|ฅ||kho khon (person) [obs]||kh||k||kʰ||k||L||ค|
|ฆ||kho ra-khang (bell)||kh||k||kʰ||k||L||น|
|ง||ngo ngu (snake)||ng||ng||ŋ||ŋ||L|
|จ||cho chan (plate)||ch||t||tɕ||t||M||จ|
|ฉ||cho ching (cymbals)||ch||-||tɕʰ||-||H|
|ช||cho chang (elephant)||ch||t||tɕʰ||t||L||ข|
|ซ||so so (chain)||s||t||s||t||L||ข|
|ฌ||cho choe (bush)||ch||-||tɕʰ||-||L|
|ญ||yo ying (woman)||y||n||j||n||L|
|ฎ||do cha-da (headdress)||d||t||d||t||M|
|ฏ||to pa-tak (goad)||t||t||t||t||M|
|ฐ||tho san-than (base)||th||t||tʰ||t||H|
|ฑ||tho nangmon-tho (dancer)||th||t||tʰ||t||L||ท|
|ฒ||tho phu-thao (old person)||th||t||tʰ||t||L|
|ณ||no nen (novice monk)||n||n||n||n||L|
|ด||do dek (child)||d||t||d||t||M||ค|
|ต||to tao (turtle)||t||t||t||t||M||ค|
|ถ||tho thung (sack)||th||t||tʰ||t||H||ก|
|ท||tho thahan (soldier)||th||t||tʰ||t||L||ท|
|ธ||tho thong (flag)||th||t||tʰ||t||L|
|น||no nu (mouse)||n||n||n||n||L||น|
|บ||bo baimai (leaf)||b||p||b||p||M||บ|
|ป||po plaa (fish)||p||p||p||p||M||บ|
|ผ||pho phueng (bee)||ph||-||pʰ||-||H||ผ|
|ฝ||fo fa (lid)||f||-||f||-||H||ผ|
|พ||pho phan (tray)||ph||p||pʰ||p||L||ผ|
|ฟ||fo fan (teeth)||f||p||f||p||L||ผ|
|ภ||pho sam-phao (sailboat)||ph||p||pʰ||p||L|
|ม||mo ma (horse)||m||m||m||m||L||น|
|ย||yo yak (giant)||y||y||j||j||L||ข|
|ร||ro ruea (boat)||r||n||r||n||L|
|ล||lo ling (monkey)||l||n||l||n||L||ล|
|ว||wo waen (ring)||w||w||w||w||L|
|ศ||so sala (pavilion)||s||t||s||t||H||ค|
|ษ||so rue-si (hermit)||s||t||s||t||H||บ|
|ส||so suea (tiger)||s||t||s||t||H||ล|
|ห||ho hip (chest)||h||-||h||-||H||ท|
|ฬ||lo chu-la (kite)||l||n||l||n||L||ผ|
|อ||o ang (basin)||**||-||ʔ||-||M||อ|
|ฮ||ho nok-huk (owl)||h||-||h||-||L||อ|
* Consonant-vowel combination characters, not members of any group.
** อ is a special case in that at the beginning of a word it is used as a silent initial for syllables that start with a vowel (all vowels are written relative to a consonant — see below). The same symbol is used as a vowel in non-initial position.
Thai vowel sounds and diphthongs are written using a mixture of vowel symbols, consonants, and combinations of vowel symbols. Each vowel is shown in its correct position relative to an initial consonant (indicated by a dash "–") and sometimes a final consonant as well (second dash). Note that vowels can go above, below, left of or right of the consonant, or combinations of these places. If a vowel has parts before and after the initial consonant, and the syllable starts with a consonant cluster, the split will go around the whole cluster.
The pronunciation is indicated by the International Phonetic Alphabet and the Romanisation according to the Royal Thai Institute as well as several variant Romanisations often encountered. A very approximate equivalent is given for various regions of English speakers and surrounding areas.
|–||implied a||a||a||u||u in "nut"|
|– –||implied o||o||o||oa in "boat"|
|–รร–||ro han *||ɑ||a||u||u in "nut"|
|–ว–||wo waen *||ua||ua||uar||ewe in "newer"|
|–วย||sara uai||uɛj||uai||uay||uoy in "buoy"|
|–อ||sara o||ɔː||o||or, aw||aw in "saw"|
|–อย||sara oi||ɔːj||oi||oy||oy in "boy"|
|–ะ||sara a||aʔ||a||u||u in "nut"|
|–ั –||mai han-akat||a||a||u||u in "nut"|
|–ัย||sara ai||ɑj||ai||i in "hi"|
|–ัว||sara ua||ua||ua||ewe in "newer"|
|–ัวะ||sara ua||uaʔ||ua||ewe in "sewer"|
|–า||sara a||aː||a||ah, ar, aa||a in "father"|
|–าย||sara ai||aːj||ai||aai, aay, ay||ye in "bye"|
|–าว||sara ao||aːw||ao||au||ow in "now"|
|–ำ||sara am||ɑm||am||um||um in "sum"|
|–ิ||sara i||i||i||y in "greedy"|
|–ิว||sara io||iw||io||ew||ew in "new"|
|–ี||sara i||iː||i||ee, ii, y||ee in "see"|
|–ึ||sara ue||ɯ||ue||eu, u, uh||u in French "du" (short)|
|–ื||sara ue||ɯː||ue||eu, u||u in French "dur" (long)|
|–ุ||sara u||u||u||oo||oo in "look"|
|–ู||sara u||uː||u||oo, uu||oo in "too"|
|เ–||sara e||eː||e||ay, a, ae, ai, ei||a in "lame"|
|เ–็ –||sara e||e||e||e in "neck"|
|เ–ะ||sara e||eʔ||e||eh||e in "neck"|
|เ–ย||sara oei||ɤːj||oei||oey||u in "burn" + y in "boy"|
|เ–อ||sara oe||ɤː||oe||er, eu, ur||u in "burn"|
|เ–อะ||sara oe||ɤʔ||oe||eu||e in "the"|
|เ–ิ –||sara oe||ɤ||oe||eu, u||e in "the"|
|เ–ว||sara eo||eːw||eo||eu, ew||ai + ow in "rainbow"|
|เ–า||sara ao||aw||ao||aw, au, ow||ow in "cow"|
|เ–าะ||sara o||ɔʔ||o||orh, oh, or||o in "not"|
|เ–ีย||sara ia||iːa||ia||ear, ere, ie||ea in "ear"|
|เ–ียะ||sara ia||iaʔ||ia||iah, ear, ie||ea in "ear" with
|เ–ียว||sara iao||io||iao||eaw, iew, iow||io in "trio"|
|เ–ือ||sara uea||ɯːa||uea||eua, ua, ue||ure in "pure"|
|เ–ือะ||sara uea||ɯaʔ||uea||eua, ua||ure in "pure"|
|แ–||sara ae||ɛː||ae||a||a in "ham"|
|แ–ะ||sara ae||ɛʔ||ae||aeh, a||a in "at"|
|แ–็ –||sara ae||ɛ||ae||aeh, a||a in "at"|
|แ–ว||sara aeo||ɛːw||aeo||aew, eo||a in "ham" + ow in "low"|
|โ–||sara o||oː||o||or, oh, ô||o in "go"|
|โ–ะ||sara o||oʔ||o||oh||o in "poke"|
|ใ–||sara ai mai muan||ɑj||ai||ay, y||i in "I"|
|ไ–||sara ai mai malai||ɑj||ai||ay, y||i in "I"|
|ฤ||ro rue (short) *||rɯ||rue||ru, ri||ri in "Krishna"|
|ฤๅ||ro rue (long) *||rɯː||rue||ruu|
|ฦ||lo lue (short) *||lɯ||lue||lu, li||li in "Lima"|
|ฦๅ||lo lue (long) *||lɯː||lue||lu|
* vowels or diphthongs written with consonant symbols
Diacritics are used with the Thai alphabet to indicate modifications of the values of the letters.
Thai is a tonal language and the script gives full information on the tones. Tones are realised in the vowels, but indicated in the script by a combination of the class of the initial consonant (high, mid or low), vowel length (long or short), closing consonant (unvoiced/plosive or voiced/sonorant) and sometimes one of four tone marks. The names and signs of the tone marks are derived from the numbers one, two, three and four in an Indic language. The rules for denoting tones are shown in the following chart:
|tone of syllable||initial consonant|
|sign||Thai||RTGS||syllable composition||high class||mid class||low class|
|(เปล่า)||(none)||long vowel or vowel plus sonorant||rising||mid||mid|
|(เปล่า)||(none)||long vowel plus plosive||low||low||falling|
|(เปล่า)||(none)||short vowel at end or plus plosive||low||low||high|
Mai chattawa and mai tri are only used with mid-class consonants.
The letter ห (high class) is used as a silent letter before certain low-class consonants (Nasals ง, ญ, น and ม; and non-plosives ว, ย, ร and ล; all of which have no corresponding high-class phonetic match) to give that consonant the tone properties of a high-class consonant. In polysyllabic words, an initial high class consonant with an implicit vowel renders the following syllable also high class. In four cases, อ (mid-class) is placed before ย (low-class) to give mid-class tone rules.
There are a few exceptions to this system, notably the pronouns chan and khao, which are both pronounced with a high tone rather than the rising tone indicated by the script (in an informal conversation; generally when these words are recited or read in public, they are pronounced in rising tone).
Other diacritics are used to indicate short vowels and silent consonants:
|–็||mai taikhu||shortens vowel|
|–์์||thanthakhat, mai karan||indicates silent letter|
- "The origins of the Thai typewriter". Retrieved 2008-02-20.