🍷 SO2 Wine Calculator
Calculate how much potassium or sodium metabisulfite to add to your wine to raise free SO2 from its current level to your target level.
What this calculator does
Free sulfur dioxide (SO2) is what protects wine from oxidation and spoilage organisms. Home and small-scale winemakers commonly test free SO2 with a titration kit or meter, then top it back up to a target level using potassium metabisulfite (KMS) or sodium metabisulfite (SMS) powder. This calculator works out exactly how much powder to add.
How the math works
KMS is roughly 57.6% SO2 by weight, and SMS is roughly 67.4% SO2 by weight – the rest is inert carrier compound. To raise free SO2 by a certain number of parts per million (mg per liter) across your batch volume, the calculator finds the total milligrams of pure SO2 needed, then divides by the compound’s SO2 fraction to find how many grams of powder to weigh out.
- Typical target free SO2 for finished red wine: 20-30 ppm
- Typical target free SO2 for finished white/rosé wine: 25-40 ppm
Always measure your actual free SO2 with a test kit before dosing, since the correct target depends on your wine’s pH and style. This tool is for general home-winemaking planning and does not replace laboratory analysis.