The effectiveness of sulfite is extremely sensitive to pH. As the pH of your wine rises, you need significantly more Free SO2 to maintain the same level of protection.
Temperature Adjustment: The pH effectiveness changes with temperature. The calculator adjusts the chemistry based on the fact that SO2 is more effective (but more volatile) at higher temperatures.
The "Target" is not arbitrary; it is based on the microbial stability needs of the specific wine style:
White/Rosé (0.8 mg/L Molecular): Whites usually have lower tannin levels and higher risks of browning or refermentation, requiring a higher level of protection.
Red Wine (0.5 mg/L Molecular): Reds have natural protection from tannins and polyphenols so a lower threshold is used.
Alcohol acts as a preservative. When alcohol is present, it "stresses" the cell membranes of spoilage organisms, meaning you don't need quite as much SO2 to get the job done.
The Logic: The calculator applies an inverse factor: 1 + (0.01 * ABV).
Result: A wine at 14% ABV will show a slightly lower "Recommended Free SO2" than a wine at 10% ABV, even if the pH is identical.
Once the Target Free SO2 is determined, the calculator determines the physical weight of powder needed.
Available SO2: KMS powder is not 100% sulfur; it is roughly 57% available SO2 by weight.
To make it user-friendly, the calculator performs an internal conversion if you select "Gallons" instead of "Liters":
Multiplier: Gallons * 3.78541
This ensures that the metric-based chemical formulas still produce an accurate result for standard US carboys and barrels.