🍷 Sulfur (SO2/Sulfite) Calculator for Winemaking
Work out how much potassium metabisulfite (or how many Campden tablets) to add to reach a target free SO2 level in your batch.
How sulfite additions are calculated
Potassium metabisulfite (KMS) is about 57.6% available sulfur dioxide (SO2) by weight, so 1 gram of KMS added to a batch releases roughly 576mg of SO2. This calculator finds how much extra SO2 (in ppm, which is the same as mg per liter) you need to reach your target, multiplies that by your batch volume in liters to get total milligrams of SO2, and divides by 576 to get grams of KMS.
Why free SO2 matters and why real results vary
Free SO2 is the portion of added sulfite that stays active in your wine or cider, protecting it from oxidation and spoilage microbes; some of what you add will bind to other compounds in the liquid and stop being "free," so actual measured free SO2 after mixing can be lower than this theoretical calculation, especially in musts high in sugar or with high pH.
- 1g potassium metabisulfite ≈ 576mg available SO2
- 1 standard Campden tablet ≈ 0.44g potassium metabisulfite
- Typical target for stable finished wine: 25-50 ppm free SO2, depending on pH
This is a general homebrewing and food-preservation planning tool for educational purposes; always verify free SO2 with test strips or lab measurement, and follow your local regulations for sulfite labeling if selling any product.