Wine Sulfite Dosage Calculator
When a wine has been exposed to air, tested after racking, or simply left sitting longer than planned, the free SO₂ reading tells you how much of the protective reserve is still available. Potassium metabisulfite, usually shortened to KMBS, is the cellar powder used to restore that reserve. This calculator takes the batch volume, the current free SO₂ level, the target free SO₂ level, and the powder purity, then turns them into a weight you can actually measure on a scale. The point of the page is to keep the arithmetic tied to the wine in front of you. Instead of relying on a rule of thumb that ignores batch size, the calculator scales the adjustment to the liters you enter and the size of the gap between your current and desired readings. That makes it useful for a test jug, a small carboy, a barrel, or a larger tank as long as the values are entered in liters, mg/L, and percent purity. Free SO₂ is the portion of sulfur dioxide that is still available to do protective work in the wine. It is the figure that matters when you compare a lab reading to a cellar target, because that active reserve is what helps slow oxidation and many spoilage pathways. Potassium metabisulfite (KMBS) is the common powder used to raise free SO₂. Once dissolved, it releases sulfur dioxide into the wine, which is why a very small addition can have a measurable effect on the reading. The calculator assumes the wine is well mixed and that the current value represents the batch as a whole rather than one isolated sample from the top or bottom of a vessel. The calculator uses a straightforward mass-balance relationship. The dose rises with batch volume and with the difference between the target and current free SO₂ readings, then falls as the product purity increases. With purity entered as a percentage, the relationship used by the calculator is: If you want to check the dose by hand, the same relationship can be split into smaller pieces before it is recombined into the final gram amount. Where: The calculator does not ask you to convert units by hand. It already treats the free SO₂ values as mg/L, the batch size as liters, and the purity field as a percentage, so the expression above is the same one the form uses behind the scenes. Suppose you have 100 liters of wine with a current free SO₂ reading of 10 mg/L and you want to move it to 30 mg/L. With the purity field left at 57%, the calculator treats the adjustment as a 20 mg/L rise across the entire batch. First, the wine needs 2.0 grams of actual SO₂ to bridge that gap across 100 liters. After correcting for the fact that only part of the powder is active metabisulfite, the required KMBS addition comes out to about 3.51 grams. This is the kind of result a dosing tool should provide: a small, specific weight tied to one batch and one target, rather than a cellar rule that ignores the readings you already measured. If your batch is larger or smaller, or if your powder purity is different, the same formula scales immediately. Use the example as a check on the direction of the math. A larger volume increases the gram requirement, a wider free SO₂ gap increases the gram requirement, and a stronger powder reduces the gram requirement because more of each gram is active. If you are still deciding what to enter as your desired level, think about the style of wine, how much oxygen it is likely to see, and how long it will sit before bottling. Lighter wines and wines that need more protection usually call for a higher target than sturdier batches that will be handled less often. Use the table below as a planning reference for choosing a target, not as a substitute for your own cellar practice or lab measurements. The table is a style guide, not a dosage chart. Once you choose the target that makes sense for the wine, the calculator converts the free SO₂ gap into grams of KMBS for that batch. Free SO₂ is the protective reserve winemakers watch after testing a batch. This calculator turns the gap between the current reading and the target reading into a KMBS weight so you can dose with a scale instead of a guess. Yes. The calculation scales directly with the liters you enter, so the same formula works for a small carboy, a barrel, or a larger tank as long as the wine is measured in liters. Use the purity printed on the bag or supplier sheet if you have it. The default 57% field is a common starting point, but the result is most useful when the purity matches the product you actually plan to add. KMBS is a standard cellar addition when it is handled carefully, but sulfite sensitivity is real. Follow your usual safety practices and any local labeling or usage rules that apply to your wine. Retest after you dose and mix, then check again as the wine ages or sees new oxygen exposure. Free SO₂ is not fixed forever, so the target may need to be refreshed later. No. It only converts the free SO₂ adjustment into a KMBS dose. Bound SO₂ and any pH-based cellar decision remain outside the calculator's scope. A wine sulfite addition is usually made when a batch needs more protection than its current free SO₂ reserve can provide. The added KMBS helps defend against oxidation, slows the growth of unwanted microbes, and keeps aroma from fading too quickly during storage. That matters most after racking, filtering, bottling, or any other step that leaves the wine more exposed to air. Because the same powder dose can mean very different things in a 19 L carboy versus a 600 L tank, the calculator is built to scale the addition to the actual batch in front of you. It does not replace lab testing; it turns the result into a practical weighing target. Start with a measured current free SO₂ value, then decide what target you want for this wine style or stage of aging. Enter the volume in liters, the current level, the desired level, and the KMBS purity percentage. The calculator then returns grams of powder to weigh out. where is the KMBS dose in grams, is the volume in liters, is the target free SO₂ level, is the current level, and is the purity percentage. The form uses the same relationship internally, so the result you get is the amount needed to bridge the gap between the two readings you entered. Notice how the dose rises with volume and with the size of the free SO₂ increase, while higher purity reduces the grams required. If your wine is especially sensitive to oxygen or you are planning a long hold before bottling, double-check the target you choose before calculating the addition. Pairing sulfite tracking with other planning tools can make cellar work easier. The fruit wine ABV calculator and the wine fermentation schedule calculator help with adjacent winemaking decisions, while the solar food dehydrator area calculator covers the preservation side of a harvest project outside the winery.
Stephanie Ben-JosephIntroduction to Wine Sulfite Dosage
Understanding Free SO₂ and Potassium Metabisulfite in Wine
Formula for Calculating a Wine Sulfite Dose from Free SO₂
Worked Example: Raising a 100 L Wine Batch from 10 to 30 mg/L
Free SO₂ Target Ranges by Wine Style
Wine Type Typical Free SO₂ (mg/L) Purpose Red Wine 10–30 Protection against oxidation and spoilage White Wine 25–50 Higher protection due to lighter color and sensitivity Rosé Wine 20–40 Balance between red and white wine protection Sparkling Wine 30–50 Prevent microbial growth during secondary fermentation Limitations and Assumptions for Wine Sulfite Dosing
Wine Sulfite Dosage Calculator FAQ
Why is sulfite dosing important in winemaking?
Can I use this calculator for any wine volume?
What if I don’t know the purity of my potassium metabisulfite?
Is it safe to add sulfites to wine?
How often should I measure free SO₂ levels?
Does this calculator account for bound SO₂?
Why Add Sulfites to Wine?
How to use: Turning a Free SO₂ Test into a KMBS Weight
Example Dosage Table
Volume (L) Current (mg/L) Desired (mg/L) Purity (%) Dose (g) 20 10 30 57 0.70 23 15 35 57 0.81 50 20 40 55 1.82
Arcade Mini-Game: Wine Sulfite Dosage Calculator Calibration Run
Use this quick arcade run to practice separating useful scenario inputs from common planning mistakes before you rely on the calculator output.
Start the game, then use your pointer or arrow keys to catch useful inputs and avoid bad assumptions.