Rieslings are made in a wide range of sweetness levels, ranging from bone-dry (no residual sugar) to late-harvest or dessert wines with a LOT of residual sugar, as high as 20% or so. A few wineries show the sweetness level (such as dry, off-dry, semi-sweet, sweet) on a scale on the back label. However, very few labels will tell you what the residual sugar percentage actually is.

If the back label doesn't give any such clues, look at the alcohol percentage on the label. Because alcohol comes from yeast fermenting the sugar in the grape juice, a higher alcohol percentage means less remaining sweetness.

Dry rieslings are a popular style at present. I prefer about 1.0 to 1.5% residual sugar (RS) in a Riesling or similar wine, like Gewurztraminer; that would be considered off-dry.