I have seen many different scales, but I do not know if there is an internationally agreed upon answer...here is a link to the labelling requirements per country, so you can see if each country has a specific ruling... http://www.icap.org/table/alcoholbeveragelabeling
Here is an example from the Missouri Winemaking Society Fair page for 2012...
I. DRY WINES – Wines that have virtually no residual sugar (less than 0.5%). Specific gravity is < 1.000. Wines entered in this category have complete fermentation (not stopped by intervention of the winemaker) and have not been back-sweetened.
II. OFF-DRY WINES - Used to accompany a meal’s main course or drink by themselves. These wines are not completely dry (i.e., may be back sweetened or may have early termination of fermentation), but are too dry for a Social Wine. They have up to 1% residual sugar and less than 14% alcohol. Specific gravity is 1.000 to 1.010.
III. SOCIAL WINES - Primarily enjoyed in the evening or afternoon with snacks, but may be used with meals or any time. They typically have 1% to 4.0% unfermented sugar with less than 14% alcohol. These are commonly known as "semi-dry" or "semi-sweet" wines. Specific gravity is 1.010 to 1.025.
IV. DESSERT WINES - Full bodied, very sweet wines that are normally served at the end of a meal or with desserts or snacks. These wines contain more than 4.0% sugar and may contain over 14% alcohol. These are commonly referred to as "sweet" wines. Specific gravity is > 1.025.
V. SPECIALTY WINES - Includes sparkling (carbonated) wines, appetizer or cocktail wines (such as sherry, vermouth, Madeira and port), honey-based wines, and other wines which do not fit the other categories. A fortified wine (Port, Sherry or Madeira) is a wine that uses distilled spirits to increase alcohol level.
This is a table from 2012 Wisconsin State Fair..
- wine with a final specific gravity of 1.002 or less is considered dry.
- wine with a final specific gravity of 1.003 to 1.010 is considered semi-sweet.
- wine with a final specific gravity above S.G.1.010 is considered sweet.