Sulfite Calculator for Wine

Sulfur dioxide (SO₂) protects wine from oxidation and from wild yeast and bacteria. Home winemakers add it as potassium metabisulfite, either as a powder or pressed into Campden tablets. Enter your batch size and the dose you want below to get grams of powder and an approximate tablet count, plus the free SO₂ level your wine should hold at its pH.

Doses here are in parts per million (ppm), which is the same as milligrams per liter.

How the Sulfite Calculator Works

Grams of potassium metabisulfite

Potassium metabisulfite (K-meta, or KMBS) is not pure SO₂. Oklahoma State University Extension’s fact sheet Understanding Free Sulfur Dioxide (FSO2) in Wine gives the calculation as the desired ppm multiplied by the volume in liters, divided by 0.57, which is the share of the powder that becomes SO₂. The calculator uses the same 0.57 factor and converts milligrams to grams, so for 5 gallons (about 18.9 liters) at 50 ppm it returns 1.66 grams.

Campden tablets

Campden tablets are pressed metabisulfite, sold as an easier way to dose small batches. How strong one tablet is depends on the brand. North Mountain Supply’s Campden tablet listing says one tablet in one gallon of must yields 75 ppm total SO₂, while North Dakota State University Extension’s Getting Started With Home Winemaking (FN1638) pairs one tablet per gallon with a dose of 50 ppm. Tablet weights vary too. The Campden tablet reference entry describes a typical tablet as 0.44 grams of metabisulfite plus filler, about 67 ppm SO₂ in a US gallon; Northern Brewer’s Campden tablet listing rates its tablets at 75 ppm per gallon, which by the Oklahoma State formula corresponds to about 0.50 grams of potassium metabisulfite. The calculator lets you pick either strength and counts tablets to the nearest half. Treat the tablet count as approximate, and weigh powder when the dose matters.

Some tablets sold as Campden are sodium metabisulfite rather than potassium. Both release SO₂; check the label for which one you have and for the maker’s dose.

Free SO₂ and wine pH

Only part of the SO₂ you add stays free, and only a small share of the free SO₂ is in the molecular form that actually protects the wine. The Oklahoma State fact sheet explains that this share depends on pH: the more acidic the wine, the more of the free SO₂ is molecular. Winemakers aim for 0.8 ppm molecular SO₂, and the third result in the calculator is the free SO₂ that gives 0.8 ppm molecular at the pH you enter.

Free SO₂ Needed by pH

The first two columns are from the Oklahoma State University Extension chart of free SO₂ forms. The calculator’s estimate uses the molecular percentage in the middle column; the chart’s recommended free SO₂ in the last column sits about ten percent higher, which gives a little margin.

Two things stand out. Low-acid wines need a lot more SO₂ for the same protection, and above about pH 3.8 the numbers climb fast. The same fact sheet notes that adjusting the pH before an SO₂ addition is sometimes necessary.

The calculator does not know what is already in the wine

The dose you add is not the free SO₂ you end up with. Some of it binds to compounds in the wine straight away, and earlier additions may still be present. Oklahoma State recommends double-checking every calculation, recording each addition and monitoring free SO₂ until bottling. Without a test kit, follow your recipe’s dose rather than chasing a number in the table.

Quick Dose Chart

Grams of potassium metabisulfite powder for common doses and batch sizes, from the same formula as the calculator. Tablet counts assume the typical 0.44 gram tablet, rounded to the nearest half.

For a 6-gallon batch, LD Carlson’s instructions on its potassium metabisulfite listing say to use one quarter teaspoon, dissolved in warm water before adding. A kitchen scale that reads to 0.01 gram is the more accurate route.

When to Add Sulfite

Before fermentation

With fresh fruit or crushed grapes, NDSU’s FN1638 adds 50 ppm (or one Campden tablet per gallon) to the juice to suppress wild yeast and bacteria, then waits about 24 hours before adding the winemaking yeast. Home Brew Ohio’s Campden tablet listing gives the same 24-hour wait.

At racking

NDSU suggests additional Campden tablets or SO₂ at every other racking, following the recipe, to protect the wine from oxygen exposure and spoilage.

Before bottling

This is the addition the pH table matters most for, because the wine will sit in the bottle for months. Check the pH if you can, use the calculator, and stir the addition in thoroughly so it mixes through the whole batch, as the Oklahoma State fact sheet advises. Our guide to bottling and corking homemade wine covers the rest of the routine.

Related Tools and Guides

• Campden tablets vs potassium metabisulfite, the full guide.
• Wine ABV calculator.
• Sugar calculator.
• Home wine making equipment and supplies.