Two conventions, one number, different answers
Salt percentage in vegetable fermentation is expressed two different ways and sources rarely say which they mean.
Percent of total weight takes the vegetables and the water together as the base. This is the convention used for packed ferments where the vegetable is shredded or cut small and the brine is partly liquid the vegetable itself releases — sauerkraut, kimchi, chopped vegetable ferments. It makes sense there because the vegetable's own water becomes part of the brine, so counting the vegetable in the base approximates the liquid the salt will eventually be dissolved in.
Percent of the water takes only the added water. This is the convention for a covering brine poured over whole or large-cut items — cucumbers, olives, whole peppers — where the vegetable stays largely intact and the brine is mostly what you poured in.
Take 2 kg of vegetables and 2 kg of water at 3%. The total-weight method gives 120 g of salt. The water-only method gives 60 g. That is a factor of two on the same recipe from the same words, and it is why a ferment sometimes comes out inexplicably salty or inexplicably soft. Whichever your source means, the fix is the same: work out which base it is using, and be explicit in your own notes.
The finer point about what the percentage divides by
There is a second ambiguity underneath the first. When a recipe says 3% salt, does it mean the salt weighs 3% of the food and water, or 3% of the finished mixture including the salt itself? For 4000 g of food and water, the first reading gives 120 g and the second gives 4000 x 3 / 97, which is 123.7 g. The difference is small at ordinary percentages and grows as the percentage does.
Almost everyone means the first, and the calculator defaults to it. The distinction is worth knowing about because it explains small discrepancies between sources that are otherwise saying the same thing, and because at the higher salt levels used for long-term preservation the gap stops being negligible.
Weigh the salt
Salt is sold in wildly different grain sizes and they do not measure the same by volume. A tablespoon of fine table salt weighs roughly twice what a tablespoon of coarse flake salt does. Any recipe that specifies salt in spoons has either been written for one specific product or has not thought about it, and following it with the wrong salt is a large error in a variable that matters.
Weight is unambiguous, which is why every source that takes the subject seriously gives grams. Buy a scale that reads to a gram, weigh the vegetables, weigh the water, weigh the salt. It is faster than measuring by volume once you stop reaching for spoons.
Salt type matters in a second way. Some table salts carry anti-caking agents and added iodine. Whether that affects a ferment is argued about more than it is measured, and the practical answer is to use whatever your source assumes, so that if something goes wrong you have changed one variable fewer.
| Ferment style | Usual convention | Why |
|---|---|---|
| Sauerkraut, kimchi, shredded vegetables | Percent of total weight | Little or no added water; the vegetable supplies the brine |
| Whole cucumbers, olives, whole chillies | Percent of the water | Vegetables stay intact; the poured brine is the medium |
| Chopped vegetables in a covering brine | Either, and sources disagree | Both liquids contribute; read the source carefully |
Safety, stated once and properly
Fermentation safety is not a calculation. It depends on salt concentration, on acidity developing quickly enough, on temperature, and on the food staying fully submerged beneath the brine where the organisms you want can outcompete the ones you do not. Botulism risk is real in low-acid anaerobic conditions, which is exactly the environment a sealed jar of vegetables creates. Canning and preserving are a separate discipline again, with tested processes that exist because they were validated and that must be followed rather than adapted.
This page will not tell you a safe salt percentage, a safe pH or a safe time, because those numbers belong to a tested procedure for a specific food and are not transferable between recipes. Get the process from a current tested source — a university extension food preservation program, or the national home food preservation guidance — and use this calculator to execute the percentage that source specifies, accurately and in grams.
The general food handling that surrounds all of this is covered in the food safety guide, and how long things last once they are made is in fridge storage times.
Elsewhere on the site
For the other kind of fermentation, the ABV and attenuation calculator and the fermentation temperature calculator deal with yeast rather than lactic bacteria, and temperature control matters for both. If you are scaling a written recipe rather than working from percentages, the recipe scaler handles the multiplication and the cooking unit converter handles the units. For bread, where percentages are also taken against a single reference weight, the baker's percentage calculator uses the same idea with flour as the base.
Questions people ask
My recipe says 2% salt and does not say of what. Which should I use?
Look at what the ferment is. If the vegetable is shredded or chopped small and there is little or no added water — kraut, kimchi, a chopped vegetable ferment — the percentage is almost certainly of the total vegetable weight, because that is the only weight in the recipe. If whole items sit in a poured brine, it is almost certainly of the water. Where a recipe has both a significant vegetable weight and a significant water weight and does not say, the sensible move is to find another source that is explicit rather than guess, since the two readings can differ by a factor of two.
Do I count the weight of the water the vegetables release?
Not in the calculation, because you cannot know it in advance. A shredded vegetable can give up a large fraction of its weight as liquid over a day or two, which is precisely why the total-weight convention exists for those ferments — counting the vegetable in the base is a rough way of counting the water it is about to become. For a covering brine over whole items the release is much smaller and slower, and the water-only convention accepts that the brine will dilute a little over time.
Does it matter what kind of salt I use?
For the arithmetic, no — salt is salt by weight and this calculator does not care. For the ferment, use what your source assumes rather than substituting, so that if something goes wrong you have one fewer unknown. The practical trap is grain size: fine and coarse salts differ by around a factor of two by volume, so a recipe written in spoons for one salt is badly wrong with another. Weigh in grams and the problem disappears entirely.
Why does the calculator not just tell me what percentage to use?
Because a safe percentage is not a general fact — it belongs to a tested procedure for a specific food at a specific temperature, alongside the acidity that develops and how long the process runs. Publishing a number here that someone applied to a different vegetable, at a different temperature, for a different length of time, would be worse than publishing nothing. Salt concentration, acidity, temperature and keeping the food under the brine work together, and the combinations that have been tested are documented by extension food preservation programs and by the national home food preservation guidance. Take the percentage from there and bring it here.
Can I use this for a brine I am going to can afterwards?
You can use it to weigh out a brine, but canning is a separate discipline and this page does not cover it. Processing times, jar sizes, headspace, acidity and method are all part of a tested procedure, and altering any of them — including the recipe you filled the jar with — invalidates the process that time was validated against. If the plan involves a canner, get the whole procedure from a current tested source and follow it as written rather than assembling it from parts.