I just called McDonalds nutrition headquarters and they told me that they don't have or provide the calorie info for the sweet tea. The best we would be able to do is use a calorie count for a generic sweet tea, though that's still kind of iffy since we don't know how much sugar they put in it. I live in the South where sweet tea is a household staple

and we make it with 1/2 cup up to 1 cup sugar per 2 quarts of water. That would equal as much as 387 calories per quart, or 97 calories per 8 oz cup at most However, the large sweet tea is a whole quart. Ice could take up about 1/3 of that or more, though.
So 1 large sweet tea at mcd potentially contains 387 cal or 8 points without ice. Or half that amount if they (hopefully) go the lower route.
The man I spoke with said he would pass along the request to include sweet tea nutrition info, but who knows how long that will take.
Thank goodness they offer splenda
Medium is 21 oz and small is 16 oz.