Sulphite (SO₂) Addition Calculator for Wine, Cider and Mead
Grams of potassium metabisulphite to add to reach a target free SO₂ in a given volume, after allowing for the free SO₂ already present.
Results
The dashed line marks the value you entered.
What this tool does
Potassium metabisulphite (K₂S₂O₅) releases about 57.6 % of its mass as SO₂, so each gram of SO₂ takes about 1.74 g of powder: grams = mg/L × litres ÷ 1000 ÷ 0.576. Part of what you add binds to the wine, and only the 'free' SO₂ protects it, so measure the free level with a test kit and add only the shortfall. The free SO₂ needed rises with pH, because only the molecular form does the protecting — about 0.8 mg/L molecular is a commonly quoted target for table wine. If you sell what you make, legal limits on total sulphites and labelling rules apply.
Formula
grams of K₂S₂O₅ = SO₂ to add (mg/L) × volume (L) ÷ 1000 ÷ 0.576 (powder is ≈ 57.6 % SO₂)
Variables
| Symbol | Meaning | Unit |
|---|---|---|
tg | Free SO₂ you want | mg/L |
cu | Free SO₂ already there (from a test) | mg/L |
v | Volume | L |
yl | SO₂ released by the powder (pure potassium metabisulphite ≈ 57.6) | % |
G | Potassium metabisulphite to add | g |
AD | Free SO₂ to add | mg/L |
TM | Total SO₂ added | mg |
DS | Powder per litre | mg/L |
Worked example
- Free SO₂ you want50 mg/L
- Free SO₂ already there (from a test)0 mg/L
- Volume23 L
- SO₂ released by the powder (pure potassium metabisulphite ≈ 57.6)57.6 %
- Potassium metabisulphite to add2.00 g
- Free SO₂ to add50.0 mg/L
- Total SO₂ added1150 mg
- Powder per litre86.8 mg/L
Limitations
- The result is an estimate based only on the values you type. Real situations often include factors this calculator does not know about.
- For work that must comply with a standard or be signed off, check the result against the applicable code and have it reviewed by a qualified engineer.