If your not sure if you are exempt from having a visa before travailing to Thailand, click the link and there you will find information.
Tourist Visa Exemption(“Visa Waiver Stamp”)
Visitors are eligible to enter Thailand free of charge without a visa. (NOTE: This is not ANY KIND of visa though.) Most tourists will be allowed to stay for 30 days. As of January 1st, 2017, all eligible nationalities get 30 days stay when arriving by land or air.
Visitors are now allowed only TWO visa exemptions per calendar year if arriving by LAND. The number of exemptions when arriving by air is still unlimited.
The only form to be filled out is the Arrival/Departure card that visitors will be given on the plane or at the border. If you’re eligible you’ll receive an exemption EACH TIME you enter Thailand. If you make a trip outside the country within your 30-day stay, the initial exemption is cancelled and you receive a new 30-day exemption when you return. To reiterate: If you’re eligible for an exemption, you will receive a new one each time you enter Thailand. This is not a “re-entry.”