I have seen several tables, notably,

http://winemaking.jackkeller.net/hydrom.asp

http://www.beer-wine.com/learning/how-adjust-specific-gravity

http://www.brsquared.org/wine/CalcInfo/HydSugAl.htm

But they all differ slightly. I'd like to test my hydrometer and refractometer with known gravities by adding sugar to a known volume (say 1 gallon for example) and taking measurements (like with no sugar, then the correct amount for 1.010/2.5Brix, etc), then increase the sugar and continue taking measurements, just to verify the readings. However, I can't seem to find where they are getting the numbers from for oz/gallon of sugar. Notably, Jack's table includes sugar added to water, which I believe would be the most useful, since I'll measure the water first, then add the sugar.