Thailand's visa-exemption arrangements for tourists have changed more than once in recent years, including the length of stay permitted and which passports qualify. Because this is exactly the kind of detail that goes stale fastest, we'd rather point you to how to check it than publish a number that might be wrong by the time you read this.
Before booking, check the current rules directly via your nearest Thai embassy or consulate website, or Thailand's official immigration bureau. We'll keep this page updated as an index to the right official sources rather than a static fact sheet.