Keep food and water changes separate
Suppose a recipe defines an example 2% of food plus water. With 1,000 g food and 500 g water, the amount is (1,000 + 500) × 0.02 = 30 g salt. If the water increases to 1,000 g while food stays the same, the new amount is 40 g salt.
Adding water changes the denominator. Recalculate from the new masses rather than retaining the salt amount or scaling only the food. The ratio still describes the ingredients you start with; it does not establish the concentration reached inside the food.
The food-plus-water formula
Add the mass of the food to the mass of the water, then multiply by your recipe's percentage divided by 100.
For 500 g of food, 1,000 g of water and 3%, the calculation is (500 + 1,000) × 3 ÷ 100 = 45 g salt. Here, the percentage excludes the added salt from its denominator.
Choose the denominator before calculating
Some recipes use a different convention that includes salt in the total mass. A 3% target including salt would require (500 + 1,000) × 3 ÷ 97 = 46.39 g. That is a different formula; the food-plus-water mode above follows the convention excluding added salt.
The solution-weight option in the calculator applies only to salt plus water. It does not include food. Do not switch to that option to calculate a food-inclusive total percentage.
What an equilibrium-style calculation cannot tell you
The result is an ingredient ratio. It does not establish how quickly salt moves into the food, or what concentration the finished food reaches. Thickness, temperature, composition and the process affect the outcome.
The calculator does not account for salt already in injected meat, previously salted fish, sauces or other ingredients. Use the full method from your recipe and weigh the food without its packaging or container.
Dry salting uses the same arithmetic
Set water to zero when your recipe specifies salt as a percentage of food mass alone. For 1,000 g food at 2%, the result is 20 g plain salt. This is an example, not a recommendation for curing or preservation.
Use the separate dry-salting calculator for a starting form with no added water. Neither tool calculates nitrite curing salts.