Calculator
Salt on the total weight in the vessel
Vegetable plus water, salted together. The convention that holds the concentration steady whatever the ratio.
Result
42.5g salt
Working
salt = (vegetable + water) x percent / 100 = (1.000 kg + 700.0 g) x 2.50% / 100 = 1.700 kg x 2.50% / 100 = 42.5 g This holds the concentration at 2.50% of everything in the vessel, whether the vegetable is barely covered or swimming.
Why this needs a calculator at all
Salting the vegetable and the water together fixes the concentration of the whole vessel, so a jar packed tight and a jar half full of brine ferment at the same salinity. It is not the convention the FAO bulletin uses, and it is the one most modern vegetable-fermentation writing uses, which is a common source of a factor-of-two error when a reader moves between them.
What this is not
Arithmetic, not advice. It converts the number you type; it does not know what you are fermenting, how warm your kitchen is or whether your salt is pure. Nothing on this page certifies that a preparation is safe, and no result here should be read as a recommendation to ferment at any particular strength. The published parameters, with the sentence each came from, are on the tradition pages, and what can go wrong is on safety.