Upon entering the country, as warranted by a tourist visa, permission will be granted for 60 days.
Normally, if the applicant wants to continue touring the country, an extension may be granted for not more than 30 days unless there are extenuating circumstances that would entitle the alien to a one year extension. Fee 1,900 baht.
Normally, the Immigration will extend your Tourist visa once again following the initial 30 day extension for an additional 7 days. Fee 1,900 baht.
Note that nationals of Bangladesh, China, India, Iran, Nepal, Nigeria, Pakistan, Sri-Lanka, Togo and Uganda may only extend for a further seven days.
Extension of Tourist visa (example form)