I was of the understanding that a holder of a USA Passport would be able to get a 30 stamp upon leaving Thailand and returning at the Mae Sai crossing.

Yesterday I was told that , No it would only be 15 days.....

Which are the current correct amount of days.

Not a visa runner but a tourist wanting a couple more weeks

thanks

Come to Thailand by plane you get 30 days - by land crossing a border 15 days.

Moved to the visa forum.

30 days for citizen of G7 countries both at land and air.

Be aware that if you have a history of in-out visa exempt stamps you can be denied.

30 day extensions are now given at immigrations offices for visa exempt stamps.

Moved to visa forum.

Mae Sai is turning people away that are trying to do another visa exempt entry if they have not gotten the 30 day extension that is now possible.

Perhaps that is why you were told 15 days.