This article is from the Food Preserving FAQ, by Eric Decker firstname.lastname@example.org with numerous contributions by others.
For storage of unprocessed foods at room temperature the acidity must be 5%.
** Using 5% vinegar and adding water yields LESS than a 5% pickle - this
is a VERY common error.
Salt brine must be 10% for vegetables. Sugar is often added to soften the
effects. If process or storage temperature is above 21C higher levels of
salt will be required.
For lower salt and vinegar pickling you will follow a *tested* recipe which
will specify processing.