Because Thai is written in a non-Roman script it's necessary to use a romanization system for learning Thai as a second language, unless you learn to read Thai before trying to speak it. (This is possible mostly in academic settings, such as at Berkeley where a course was developed where students learned to read Thai before learning to speak a word.) There are many systems, the most common being the academic system which includes phonetic symbols. One of the problems learning Thai is that you often have to learn a new phonetic system for each book or course. Every author, it seems, has a better idea of what a good romanization system is.
That includes the American author of the books on this website. After studying Thai myself and experiencing typical problems with pronunciation, I developed criteria for a system that would be more user-friendly than the ones I had seen. They included:
-using the English alphabet only
-not using "r" in vowels as is done in England (I wrote "aw" instead of "or" and "euh" instead of "er")
-following the system used on road signs in Thailand as much as possible (using "p/ph" and "t/th").I saw a problem with the usual "k" and "kh", though. I decided to use "g" rather than "k" for gaw-gai because it's closer to the sound of the letter, so I used "k" alone instead of the usual "kh" for the "k" sound in English. While learning Thai in Thailand I had had a problem pronouncing kai and khai ("chicken" and "egg") the same way, probably because I learned Thai myself, and not in a course. I even saw a friend get eggs in a restaurant when she thought she'd ordered chicken. The two words in this system are written gai and kai, which I believe helps to make the pronunciation of the words clearer. Similarly I used a letter "j" for jaw-jan, a sound that is often spelled with a "ch" in Thailand which confuses it with the real "ch" (chaw-ching and chaw-chang).
When this romanization system is combined with the visual tone/vowel length markers described on the next site page, I believe it creates a very accessable system that will help learners pronounce Thai correctly.
Consonants: The following have the same pronunciation as in English:b, d, f, h, k, l, m, n, s, w, ch
The following letters have different sounds from English. Two of them may be difficult for English speakers. These are the hard p sound and the hard t sound. The first is a cross between "p" and "b" while the second is a cross between "t" and "d" (like the "t" in "sixty")
a hard p/b sound
pronounced as "p" in English, not "f"
a hard t/d sound
pronounced as "t" in English, not "th"
has a harder sound than in English, between "g" and "k"
has a harder sound than in English
slightly rolled, pronounced "l" in colloquial Thai
used at the beginning of words as well as at the end
Vowels: Thai has many vowel sounds and some of them may be difficult for English speakers. Two sounds as written here may be mispronounced if read as in English. The first, the letter "a", is pronounced "ah" as in "father" so the word for house, ban, is pronounced "bahn", not "ban" as in English. Second is the single letter "o" which has the "oh" sound as in "boat". The word rot ("vehicle") is pronounced "rote". Similarly mot ("used up") is "mote" and jop ("to finish") is "jope".
as in "father"
between "ay" as in "say" and "eh" as in "met" (varies)
as in "cat"
as in "met"
as in "see"
as in "bit"
as in "Thai"
as in "saw"
as in "coat"
as in "but"
as in "boot"
the sound when you say "good" while smiling
as in "love" or "above"
Vowel Combinations: Here two or more vowel sounds are combined into one smooth sound.
ah + oh, as in "how"
aw + ee
oh + ee, as in "Chloe"
ay+ oh, as in "mayo"
ae + oh
ee + uh, as in "Pia"
ee + oh, as in "Leo"
ee + oo, as in "mew"
oo + uh, as in "Kahlua"
oo + ee, as in "Louie"
oo + ay + ee ("ay" sound turns to "ee" at the very end)
eu + uh
euh + ee
eua + ay + ee ("ay" also turns to "ee" at the end)
Notes on Pronunciation
There are differences in all languages between the ideal form and the way it's commonly spoken. Iif you study Thai in Bangkok the teacher will probably be rigorous about pronouncing "r" correctly, but when you talk to ordinary people you'll notice that they usually use "l" instead. Teachers often "prescribe" while a good course or book "describes". Following are some characteristics of informal, colloquial Thai:
1. "R" is often pronounced "l" in informal speech, for example, rong-raem ("hotel") may be pronounced long-laem.
2. "R" or "l" is omitted when it's the second consonant sound of a word. This happens in krup, the polite word that men put at the end of sentences, which is often pronounced kup. Likewise pla ("fish") may be pronounced pa.
3. In some areas of Central Thailand a "kw" or "gw" sound may be changed to an "f", for example, kwa meaning "right" (the opposite of "left") is pronounced fa, and mai gwat, meaning "broom", is mai fat ("faht").
There are further notes on pronunciation in both Essential Thai and Thai Reference Grammar.