The amounts of wine sulphur (potassium metabisulphite) to add to a wine is not a simple matter. An accurate set of scales are needed to weigh 1 or 2 grams.

Potassium metabisulphite powder when really fresh (they say within 7 days of manufacture) produces roughly 50% of its weight in free SO2 once in solution; however, this percentage reduces as the powder ages, to perhaps 35%, so a larger weight of powder needs to be added in order to achieve the required level of free SO2. For this reason it is preferable to re-measure the level of free SO2 after the addition of wine sulphur.

White wines, and sparkling wines, are treated completely differently from red wines.
Free SO2 is the important measure for white wine, only total SO2 is measured for red wine.

For white wine, a simple approach is:-

Add to the pressed juice: 10 grams of wine sulphur (Potassium metabisulphite) per 100 litres of must, to try to 'sterilize' the must and ensure that malo-lactic fermentation does not take place later. This SO2 is consumed during the fermentation process.

Then after the fermentation is complete add 8 to 10 grams per 100 litres of wine, i.e. sufficient to give about 40 to 50 milligrams per litre free SO2, which will help to prevent oxidation of the wine, until the free SO2 level falls below about 20 mgm/litre (depending on the pH of the wine).

Different vine varieties consume SO2 at different rates, so ideally it is necessary to measure the SO2 every month or so with a test such as the Sulfacor.

At bottling it is usual to adjust the free SO2 level to 30 to 35 mgm/litre (more if it is a sweet wine). The total SO2 must be below the upper limit set by European Commission regulations (EC 1493/1999 and EC 753/2002).
I find that sterilizing the bottles with SO2 solution, some hours prior to filling, adds about 5 to 8 mgm/litre free SO2 to the wine.

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