Are 3-month tourist visas in Thailand single-use only, or can I leave and re-enter during the valid period?

If you apply for a 60-day single-entry tourist visa, it is possible to obtain a re-entry permit at the immigration office or at the airport. This permit allows you to re-enter Thailand under the same visa and continue your permitted stay within the original 60-day validity period. You can also apply for a 30 days extension.

If you are eligible for a 60-day visa exemption, you will instead be granted a new exemption upon re-entry. Nevertheless, obtaining a re-entry permit may serve as an alternative to avoid multiple separate entries under different tourist visa arrangements.

Most tourist visas are issued as the single entry type. Which means once you enter, the visa is marked as used and is no longer valid.

There are multiple entry tourist visas available, but they have higher requirements to apply for, and cost quite a bit more than the single entry type.

But most people have no need for a tourist visa at all. Currently visa exempt provides the same 60 days that a tourist visa provides, so if you arrive without a visa you would get a 60 day entry stamp.