Assume the jaggery is of finest quality and is ground. Also, the sugar can be powdered or in crystal form.
I just want the same level of sweetness when I replace them with each other.
According to Cook's Info:
Jaggery is not as sweet as white sugar, so when substituting white sugar for Jaggery use about 1/3 less. When swapping Jaggery in for sugar, use anywhere from 1/4 to 1/2 more Jaggery than was called for of sugar (if you want to keep the recipe as sweet as it was.)
That meshes with my limited experience too, so if the jaggery is ground in such a way that it will measure like the sugar you are replacing, and you are replacing 1TBS of sugar, then you would want to use somewhere in the neighborhood of 1TBS plus 1tsp of jaggery. If precision is needed (which of course doesn't really apply here, but bear with me) consider that the way jaggery and sugar measures volumetrically are unlikely to really be identical. It would be better to measure by weight, or if there is liquid in the recipe, by water displacement.
well, it may be to taste that jaggery isn't as sweet as while sugar, however jaggery has a very different taste my experience is that you can use one half cup of jaggery to one cup sugar, jaggery is more rich tasting and of course has some vitamins and minerals left and some other health benefits, just experiment with your recipes,