One way to remember what the Thai consonants and their classes is to learn a little of the history of the alphabet. The Thai alphabet was developed from similar alphabets in India, where the ordering of the letters comes from arranging them in a rectangular grid according to how they are articulated by the speech organs (articulators - ฐานกรณ์). If ever I need to check that I have remembered all the letters, I write them out in a grid. A Thai friend of my wife's challenged me to recite the alphabet, and when he saw me writing the letters out in a grid, he immediately cried out "บาลี  (Pali)!"

Such a grid is given below, color-coded for the class of the consonant. The transliteration of the corresponding Sanskrit or Pali letter is shown in parentheses. Phonemic transcriptions elsewhere are placed between slanting virgules (/). Note that there is no consistent organisation by column in the last two rows. By leaving gaps, the grid preserves the order of the letters in the Thai alphabet.

The Thai alphabet has 44 letters, but I have shown all 46 of them. In the old tradition, ฤ (/reu/ - /รึ/) and ฦ (/leu/ - /ลึ/) were counted as vowels. However, when ฃ was replaced by ข (both high /kh/) and ฅ was replaced by ค (both low /kh/), ฤ and ฦ were reclassified as consonants, giving the familiar 44 consonants.

True Grid
Proto-Tai Labial (Li)	*?b	*p	*ph	*f	*b	*v		*m
Velars		ก g (k)	ข kh (kh)	ฃ kh	ค kh (g)	ฅ kh	ฆ kh (gh)	ง ng (ng)
Palatals		จ j (c)	ฉ ch (ch)		ช ch (j)	ซ s	ฌ ch (jh)	ญ y (ñ)
Retroflexes	ฎ d (ṭ)	ฏ dt (ṭ)	ฐ th (ṭh)		ฑ th (ḍ)		ฒ th (ḍh)	ณ n (ṇ)
Dentals	ด d (t)	ต dt (t)	ถ th (th)		ท th (d)		ธ th (dh)	น n (n)
Labials	บ b (p)	ป bp (p)	ผ ph (ph)	ฝ f	พ ph (b)	ฟ f	ภ ph (bh)	ม m (m)
Mere lists
Resonants		ย y (y)	ร r (r)	ฤ reu (ṛ)	ล l (l)	ฦ leu (ḷ)	ว w (v)
Others		ศ s (ç)	ษ s (ṣ)	ส s (s)	ห h (h)	ฬ l (ḷ)	อ   ( )	ฮ h

Encoding:	High	Mid	Low

If you suffer from red-green colour blindness, note that the high consonants are those in the columns headed *ph and *f, and the first four in the row entitled 'others'.

Although some people assert that Pali is most authentically rendered in a Devanagari alphabet, it is generally believed that Pali has never had its own alphabet. Pali has always been rendered in local languages of Thailand, Burma, or Sri Lanka. Let's examine the Thai consonants used in Pali:

ก	ข	ค	ฆ	ง
จ	ฉ	ช	ฌ	ญ
ฏ	ฐ	ฑ	ฒ	ณ
ต	ถ	ท	ธ	น
ป	ผ	พ	ภ	ม
ย	ร	ล	ว	ส	ห	ฬ	อํ

If you compare the tables, you can see that Thai created nine new letters, either by adding a tail to the top right hand corner or by adding a kink. In three cases, ป /bp/, ต /dt/ and ฏ /dt/, it is a bit confusing because Thai loanwords from Pali or Sanskrit generally use the new letter.

The table shows that every high letter has an equivalent low letter. Not every low letter has a corresponding high letter; the lack is made up by prefixing the high letter ห /h/. Thus the cluster หน /n/ serves as the high equivalent of น /n/. In historical terms, this is very like using a final /e/ in English to indicate a long vowel. ย /y/ is unusual. For historical reasons, it also uses the cluster อย (but only with tone mark 1, e.g. อย่า  yaa^L don't but หย่า  yaa^L divorce) as the middle equivalent of ย /y/.

One occasionally encounters transcriptions that use the Indic values, especially in official names. For example, the name of H.M. King Rama IX, ภูมิพลอดุลยเดช , which would be pronounced "phuuM miH phohnM aL doonM yaH daehtL" is normally transliterated as 'Bhumibol Adulyadej'.

Finally, you may have noticed that the Sanskrit transliterations use the symbol /ḷ/ in two different ways. One is for ฦ, which does not occur in Thai words, and is a syllabic /l/ in Sanskrit (like /le/ in 'bottle' in some pronunciations of English), and the other is for ฬ, a retroflex lateral in Pali and Sanskrit. (It occurs in Vedic Sanskrit instead of ฑ.)