For the french press, start with 55g ground coffee per litre water. Espresso - depends on what filter you have. For the double filter, try 14, 16, 18 gram, and adjust the grind appropriatly (very fine for 14 gram, quite a bit coarser for 18 gram) and see what you like
. With my filter, I have ca. 18 gram in it when I use my finger to stripe it off, and I love shots with 15 or 16 gram.
Oh yes, I recently got a digital scale too, that's how I know this