The question I get asked most often is: how much salt? The answer depends on what you're fermenting and how long you want to keep it. But there's a sensible default for most vegetables: 3 to 4 percent.
To calculate: weight of water (in grams) x salt percentage / 100 = grams of salt. For 1 litre at 3.5%: 1000 x 3.5 / 100 = 35 grams. Volume measurements are less reliable because salt density varies by grind size.
Higher salt (4–5%) is better for long-term preservation in warmth. Lower salt (2–3%) gives a faster, more active ferment with softer texture. For cucumbers I stay at 3.5%. For sauerkraut I use 2% by weight of the cabbage itself — that's a different calculation because the salt pulls liquid from the vegetable.