Calculate sulfite additions for wine. Convert between free SO₂, total SO₂, potassium metabisulfite, and Campden tablets for any volume.
Sulfite (SO₂) is one of the main tools winemakers use to limit oxidation and microbial spoilage. The challenge is dosing enough to protect the wine without overshooting the target free SO₂ level.
This calculator converts between common sulfite-addition forms such as potassium metabisulfite powder and Campden tablets. Enter the batch volume, current free SO₂, target level, and wine pH, and the page estimates the addition needed to move from the current level to the target.
Because the protective molecular SO₂ fraction changes with pH, the same free SO₂ reading can mean very different protection levels in two wines. That is why the pH-based context matters when you choose a sulfite target.
Sulfite additions are one of those cellar calculations where small arithmetic errors matter. The required addition depends on batch size, current free SO₂, target protection level, and pH, so doing it casually in your head is an easy way to underprotect or overshoot a wine.
K₂S₂O₅ to add (mg) = (target_ppm - current_ppm) × volume_L × 1.67. Campden tablets: 1 tablet = 75mg K₂S₂O₅ = ~50 ppm in 1 gallon. Molecular SO₂ = free SO₂ × (1 / (1 + 10^(pH - 1.81))). Target molecular SO₂: 0.6–0.8 ppm.
Result: 0.76g K₂S₂O₅, giving about 0.63 ppm molecular SO₂ at pH 3.4
A 20 ppm increase across 22.7 L requires 20 × 22.7 × 1.67 / 1000 = 0.76 g of potassium metabisulfite. At pH 3.4, a free SO₂ target of 35 ppm corresponds to about 0.63 ppm molecular SO₂, which is in the usual protective range for many wines.
At pH 3.0, about 6% of free SO₂ is in molecular form. At pH 3.5, only 1.5% is molecular. At pH 3.8, just 0.6%. This means a pH 3.8 wine needs 4× more free SO₂ than a pH 3.2 wine to achieve the same protection. Always factor in pH.
Key addition points: (1) at crush to suppress wild yeast, (2) after fermentation completes, (3) after MLF completes, (4) at every racking, (5) before bottling. Each addition should bring free SO₂ to the target for the wine's pH.
All fermentation produces some SO₂ naturally (5–20 ppm). "No sulfite added" wines still contain sulfites. Wines without adequate SO₂ protection have shorter shelf lives and are more prone to oxidation and microbial spoilage. Most winemakers consider SO₂ management the single most important aspect of wine quality.
Last updated:
Free SO₂ is the active protective form. Bound SO₂ has reacted with wine compounds and is no longer protective. Total SO₂ = free + bound. Only free SO₂ matters for protection.
White wines: 25–50 ppm free SO₂. Red wines: 20–40 ppm. Sweet wines: 50–70 ppm. The exact target depends on pH — higher pH needs more free SO₂ to maintain adequate molecular SO₂.
Molecular SO₂ is the truly antimicrobial fraction of free SO₂. At wine pH, only 1–6% of free SO₂ is in molecular form. Target: 0.6–0.8 ppm molecular SO₂.
At every racking, before and after MLF, before bottling, and monthly during aging. Free SO₂ declines over time as it binds to compounds in the wine.
Most people can detect SO₂ above 40–50 ppm. Sensitive individuals may notice it at 20 ppm. The legal maximum is 350 ppm in the US, but good wines rarely exceed 100 ppm total.
One standard Campden tablet contains 75mg K₂S₂O₅, which releases ~50mg SO₂. In 1 gallon, this adds ~50 ppm free SO₂. For precise dosing, weigh powder on a milligram scale.