Asking "How Many"
To ask "how many" of something, use the question word กี่ along with the classifier for that object. The structure is Noun + กี่ + Classifier.
For example, to count animals, shirts, or chairs, we use the classifier ตัว.
When building numbers greater than ten, the number one is no longer หนึ่ง. Whenever "one" is the last digit of a number (11, 21, 31, etc.), it becomes เอ็ด. Thus, eleven is สิบเอ็ด (ten-one).
Asking and Stating Age
To talk about age, use the word อายุ (age) followed by the number and the classifier ปี (year). To ask someone's age, swap the number out for กี่.
The Twenties
In Thai, the number twenty has a special form. Instead of saying สองสิบ, you must use the special word ยี่ for "two" in the twenties. So, twenty is ยี่สิบ.
Combine this with the rule for "one", and twenty-one becomes ยี่สิบเอ็ด.
Counting by Tens
For all other tens (30, 40, 50... up to 90), simply put the multiplier before the word สิบ. For instance, thirty is สามสิบ (three-tens) and ninety is เก้าสิบ (nine-tens). If there is a final digit, just add it to the end.
You can use these larger numbers to talk about quantities of items people sell (ขาย).
Prices and One Hundred
When talking about the cost of items, use the word ราคา (price) followed by the number and the Thai currency, บาท (Baht).
To say "one hundred," use the word ร้อย (hundred). One hundred is หนึ่งร้อย. Notice that the regular word for "one" (หนึ่ง) is used at the beginning of the number.
