Sulfite Addition Calculator

Use this for careful cellar records

Sulfite additions are small but important, so the calculation should be explicit and repeatable. This tool helps translate batch size and target adjustment into a practical addition amount for planning and record keeping.

Know whether you are working with free SO2, molecular SO2, or a product-rate target.
Measure pH and current SO2 where possible before deciding an addition.
Mix thoroughly and retest after the addition has had time to integrate.

Sulfite calculation notes

Sulfite additions depend on pH, wine style, legal limits, product strength, and whether you are targeting free or molecular SO2. Confirm your units before making any addition.

This calculator is for planning and checking arithmetic. For production decisions, use current lab results, calibrated measuring tools, and local winemaking regulations rather than relying only on a generic estimate.

Sulfite additions need more than arithmetic

The calculator helps convert a target adjustment into a practical addition, but sulfite management also depends on pH, wine style, free versus total SO2, product strength, and local legal limits. Confirm the units before adding anything to a batch.

For home or small-scale winemaking, the biggest risk is confusing product weight, active SO2, and solution strength. A small calculation error can become a large cellar error. Use current lab numbers, calibrated measuring tools, and careful records when moving from planning to production.

Confirm whether your target is free SO2 or molecular SO2.
Check the strength of the potassium metabisulfite product or solution.
Retest after addition before assuming the target has been reached.

Before you dose a real batch

Use the number from this calculator as a worksheet result, not as a command to add sulfite immediately. Write down the batch volume, current free SO2 test, target, product strength, and date so the next test can be compared against the same assumptions.

A practical way to use the result is to calculate first, measure twice, and add once. If the number looks surprisingly large, recheck whether the input volume is litres rather than gallons, whether the target is an increase rather than a final level, and whether the product strength is entered as active SO2 rather than total powder weight.

Best use

Checking the arithmetic before preparing a measured addition or stock solution.

Do not skip

pH, current lab results, legal limits, and a retest after mixing.

If you keep a cellar log, record the calculated addition even when you decide not to use it. Over time, those notes make it easier to see how the wine responds to topping, racking, bottling preparation, and seasonal cellar changes.

That paper trail is often more useful than memory when bottling day arrives.

How It Works

This calculator estimates sulfite additions to increase free SO2 to a chosen target.

Enter wine volume plus current and target free SO2 levels.
Set KMS SO2 strength and tablet weight assumptions.
Review SO2-equivalent requirement, grams KMS, and tablet estimate.

FAQ

Does free SO2 stay constant after addition?

Not always. Binding reactions can reduce free SO2 after dosing.

Is free SO2 the same as total SO2?

No. Free SO2 is the active protective fraction; total includes bound forms.

Should I verify analytically after dosing?

Yes. Re-testing is recommended to confirm actual achieved free SO2.