Calculate sulfite additions for wine. Convert between free SO₂, total SO₂, potassium metabisulfite, and Campden tablets for any volume.
Sulfite (SO₂) is the primary preservative and antioxidant in winemaking. Too little and the wine oxidizes or develops microbial off-flavors. Too much and it burns the nose and throat. Getting the dosage right is critical for all winemakers.
This calculator converts between different sulfite forms: potassium metabisulfite (K₂S₂O₅) powder, Campden tablets, and liquid sodium metabisulfite. Enter your wine volume, current free SO₂ level, and target levels. The calculator outputs exact weights and tablet counts.
Target free SO₂ depends on wine pH — lower pH wines (3.0–3.3) need less SO₂ because more of it exists in the active molecular form. Higher pH wines (3.5–3.8) need substantially more. The calculator adjusts recommendations based on your wine's pH to ensure adequate protection. Check the example with realistic values before reporting. Use the steps shown to verify rounding and units. Cross-check this output using a known reference case. Use the example pattern when troubleshooting unexpected results. Validate that outputs match your chosen standards.
Sulfite dosing depends on volume, current levels, pH, and wine type. Under- or over-dosing causes wine faults. A calculator ensures protection without exceeding sensory or legal thresholds. Keep these notes focused on your current workflow. Tie the context to real calculations your team runs. Use this clarification to avoid ambiguous interpretation. Align the note with how outputs are reviewed.
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: 0.63g K₂S₂O₅ or 8.4 Campden tablet quarters
Need 20 ppm increase in 22.7L: 20 × 22.7 × 1.67 / 1000 = 0.76g K₂S₂O₅. At pH 3.4, 35 ppm free SO₂ gives 0.63 ppm molecular SO₂ — adequate protection.
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.
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.