Learning the tone rules for the Thai language can seem overwhelming at first.  The tone of a syllable depends on the initial consonant class (3 choices), whether or not a tone mark is present (2 choices), vowel length (2 choices), and the syllable ending (2 choices) which would result in 24 individual rules to memorize.  Luckily this can be simplified much further.

The rules for when a tone mark is present are the simplest and were the easiest for me to remember so I’ll present those first.

1. If the initial consonant class is high or middle, then the tone matches the tone mark.
2. If the initial consonant class is low with tone mark อ่ – ไม้เอก, then the tone produced is เสียงโท or falling tone.
3. If the initial consonant class is low with tone mark อ้ – ไม้โท, then the tone produced is เสียงตรี or high tone.  

Note that the other two tone marks will never appear over a low class consonant.

The rules for when no tone mark is present are a little more complicated but are not too difficult to learn.

1. If the initial consonant class is low or middle and the syllable has a live ending then the syllable is pronounced with a middle tone.
2. If the initial consonant class is high and the syllable has a live ending then the syllable is pronounced with a rising tone.
3. If the initial consonant class is middle or  high and the syllable has a dead ending then the syllable is pronounced with a low tone.
4. If the initial consonant class is low and the syllable has a dead ending with long vowel then the syllable is pronounced with a falling tone.
5. If the initial consonant class is low and the syllable has a dead ending with short vowel then the syllable is pronounced with a high tone.

That’s it!  Only 8 rules(3 with a tone mark, 5 without a tone mark) to remember in order to read the tone of a Thai syllable correctly.  I created this simple mnemonic to help remember the rules when no tone mark is present:

Note that in Thai the adjective comes after the noun so the above would be correctly translated as “I like to eat fried crab”.  Here’s a spreadsheet I made with the Thai alphabet and the tone rules.  Check the “Tone Rules” tab.