Formal:
* ขอบคุณค่ะ (khàawp khun khâ) - This is the most polite and formal way to say thank you, used for elders, strangers, and people in positions of authority. It is used by women.
* ขอบคุณครับ (khàawp khun kráp) - The same as above, but used by men.
Informal:
* ขอบคุณ (khàawp khun) - This is a more casual and general way to say thank you, used with friends and family.
* ขอบใจ (kòawp jai) - This is a very informal way to say thank you, used with close friends.
Other phrases:
* ขอบคุณมาก (khàawp khun mâak) - This means "thank you very much".
* ขอบคุณสำหรับ... (khàawp khun sǎm-ràp...) - This means "thank you for..."
* ไม่เป็นไร (mâi bpen rai) - This means "you're welcome" and is used in response to a thank you.
It's important to choose the appropriate way to say thank you based on the situation and your relationship with the person you're speaking to.