How much sugar to add for desired OG

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Fruit Wine Alchemist
Supporting Member
Sep 6, 2020
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When I have used online calculators to determine how much sugar to add to attain my desired OG, the actual measured OG is often different from what I expect. I assumed that this would be a simple calculation, but apparently that is not so.

For my current hard lemonade, I was aiming for an OG of 1.040 in 1 gallon. I used several different online calculators, and got different results. Some of the calculators give the amount of sugar to add to 1 gallon of liquid. Others give the amount of sugar to add along with water to obtain a total volume of 1 gallon. These are not quite the same, since adding sugar increasing the volume of the water a little bit. In the figures below, I was looking for the amount of sugar to add to 1 gallon of liquid.

Here are the results In some cases I converted units, e.g. kg or oz. to lbs.
So my question is, why are these different? The calculators all refer to simply "sugar," which I take to be table sugar (sucrose).

I might need to use some distilled water and sugar to test some of these to find out which are more accurate. But it seems like that should not be necessary.
The discrepancies may have a technical cause, as a lot of the online calculators are written in Javascript, which is known for having problems with decimal calculations. Actually, a lot of programming languages have decimal inaccuracies, but Javascript is noted for it.

Some of the calculators are for beer, which has a lot more "stuff" in it that affects SG. I've noticed that formulas for beer often differ from those for wine, although I have not looked into the reasons for this.

For making additions to a must or wine, I've yet to find any calculation I completely trust. Nor do I trust calculators, as I don't necessarily know which formula the programmer used, and decimal handling inaccuracies are a problem.

I use 1 lb sugar = 2.25 cups, which changes the SG of 1 US gallon of water from 1.000 to 1.045. I typically add 3/4 of the amount of sugar, stir very well, then check SG. I'm not fussy about the exact SG, e.g., if my target is 1.090, 1.087 to 1.093 are sufficient.
I have found this chart useful. It was in the first winemaking book I ever bought. Beware, it is a British book so gallons are probably Imperial gallons.img363.jpg

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