A Thailand Tourist Visa (TR) generally allows a stay of up to 60 days per entry. The 60-day limit applies separately to each continuous stay, starting from the date of entry. If you leave Thailand and later enter again using a valid multiple-entry visa, a new stay period is calculated from the new entry date. An extension of stay may be available separately and is not included in this 60-day rule.
https://consular.mfa.go.th/th/publicservice/นักท่องเที่ยว-tourist-visa